mirror of https://github.com/python/cpython
2284 lines
76 KiB
ReStructuredText
2284 lines
76 KiB
ReStructuredText
:mod:`ast` --- Abstract Syntax Trees
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====================================
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.. module:: ast
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:synopsis: Abstract Syntax Tree classes and manipulation.
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.. sectionauthor:: Martin v. Löwis <martin@v.loewis.de>
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.. sectionauthor:: Georg Brandl <georg@python.org>
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.. testsetup::
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import ast
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**Source code:** :source:`Lib/ast.py`
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--------------
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The :mod:`ast` module helps Python applications to process trees of the Python
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abstract syntax grammar. The abstract syntax itself might change with each
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Python release; this module helps to find out programmatically what the current
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grammar looks like.
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An abstract syntax tree can be generated by passing :data:`ast.PyCF_ONLY_AST` as
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a flag to the :func:`compile` built-in function, or using the :func:`parse`
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helper provided in this module. The result will be a tree of objects whose
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classes all inherit from :class:`ast.AST`. An abstract syntax tree can be
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compiled into a Python code object using the built-in :func:`compile` function.
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.. _abstract-grammar:
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Abstract Grammar
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----------------
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The abstract grammar is currently defined as follows:
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.. literalinclude:: ../../Parser/Python.asdl
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:language: asdl
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Node classes
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------------
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.. class:: AST
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This is the base of all AST node classes. The actual node classes are
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derived from the :file:`Parser/Python.asdl` file, which is reproduced
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:ref:`below <abstract-grammar>`. They are defined in the :mod:`_ast` C
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module and re-exported in :mod:`ast`.
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There is one class defined for each left-hand side symbol in the abstract
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grammar (for example, :class:`ast.stmt` or :class:`ast.expr`). In addition,
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there is one class defined for each constructor on the right-hand side; these
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classes inherit from the classes for the left-hand side trees. For example,
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:class:`ast.BinOp` inherits from :class:`ast.expr`. For production rules
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with alternatives (aka "sums"), the left-hand side class is abstract: only
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instances of specific constructor nodes are ever created.
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.. index:: single: ? (question mark); in AST grammar
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.. index:: single: * (asterisk); in AST grammar
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.. attribute:: _fields
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Each concrete class has an attribute :attr:`_fields` which gives the names
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of all child nodes.
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Each instance of a concrete class has one attribute for each child node,
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of the type as defined in the grammar. For example, :class:`ast.BinOp`
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instances have an attribute :attr:`left` of type :class:`ast.expr`.
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If these attributes are marked as optional in the grammar (using a
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question mark), the value might be ``None``. If the attributes can have
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zero-or-more values (marked with an asterisk), the values are represented
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as Python lists. All possible attributes must be present and have valid
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values when compiling an AST with :func:`compile`.
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.. attribute:: lineno
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col_offset
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end_lineno
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end_col_offset
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Instances of :class:`ast.expr` and :class:`ast.stmt` subclasses have
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:attr:`lineno`, :attr:`col_offset`, :attr:`end_lineno`, and
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:attr:`end_col_offset` attributes. The :attr:`lineno` and :attr:`end_lineno`
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are the first and last line numbers of source text span (1-indexed so the
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first line is line 1) and the :attr:`col_offset` and :attr:`end_col_offset`
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are the corresponding UTF-8 byte offsets of the first and last tokens that
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generated the node. The UTF-8 offset is recorded because the parser uses
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UTF-8 internally.
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Note that the end positions are not required by the compiler and are
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therefore optional. The end offset is *after* the last symbol, for example
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one can get the source segment of a one-line expression node using
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``source_line[node.col_offset : node.end_col_offset]``.
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The constructor of a class :class:`ast.T` parses its arguments as follows:
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* If there are positional arguments, there must be as many as there are items
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in :attr:`T._fields`; they will be assigned as attributes of these names.
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* If there are keyword arguments, they will set the attributes of the same
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names to the given values.
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For example, to create and populate an :class:`ast.UnaryOp` node, you could
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use ::
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node = ast.UnaryOp()
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node.op = ast.USub()
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node.operand = ast.Constant()
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node.operand.value = 5
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node.operand.lineno = 0
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node.operand.col_offset = 0
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node.lineno = 0
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node.col_offset = 0
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or the more compact ::
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node = ast.UnaryOp(ast.USub(), ast.Constant(5, lineno=0, col_offset=0),
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lineno=0, col_offset=0)
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.. versionchanged:: 3.8
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Class :class:`ast.Constant` is now used for all constants.
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.. versionchanged:: 3.9
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Simple indices are represented by their value, extended slices are
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represented as tuples.
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.. deprecated:: 3.8
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Old classes :class:`ast.Num`, :class:`ast.Str`, :class:`ast.Bytes`,
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:class:`ast.NameConstant` and :class:`ast.Ellipsis` are still available,
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but they will be removed in future Python releases. In the meantime,
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instantiating them will return an instance of a different class.
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.. deprecated:: 3.9
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Old classes :class:`ast.Index` and :class:`ast.ExtSlice` are still
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available, but they will be removed in future Python releases.
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In the meantime, instantiating them will return an instance of
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a different class.
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.. note::
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The descriptions of the specific node classes displayed here
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were initially adapted from the fantastic `Green Tree
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Snakes <https://greentreesnakes.readthedocs.io/en/latest/>`__ project and
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all its contributors.
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Literals
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^^^^^^^^
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.. class:: Constant(value)
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A constant value. The ``value`` attribute of the ``Constant`` literal contains the
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Python object it represents. The values represented can be simple types
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such as a number, string or ``None``, but also immutable container types
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(tuples and frozensets) if all of their elements are constant.
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.. doctest::
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>>> print(ast.dump(ast.parse('123', mode='eval'), indent=4))
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Expression(
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body=Constant(value=123))
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.. class:: FormattedValue(value, conversion, format_spec)
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Node representing a single formatting field in an f-string. If the string
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contains a single formatting field and nothing else the node can be
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isolated otherwise it appears in :class:`JoinedStr`.
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* ``value`` is any expression node (such as a literal, a variable, or a
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function call).
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* ``conversion`` is an integer:
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* -1: no formatting
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* 115: ``!s`` string formatting
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* 114: ``!r`` repr formatting
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* 97: ``!a`` ascii formatting
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* ``format_spec`` is a :class:`JoinedStr` node representing the formatting
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of the value, or ``None`` if no format was specified. Both
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``conversion`` and ``format_spec`` can be set at the same time.
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.. class:: JoinedStr(values)
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An f-string, comprising a series of :class:`FormattedValue` and :class:`Constant`
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nodes.
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.. doctest::
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>>> print(ast.dump(ast.parse('f"sin({a}) is {sin(a):.3}"', mode='eval'), indent=4))
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Expression(
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body=JoinedStr(
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values=[
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Constant(value='sin('),
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FormattedValue(
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value=Name(id='a', ctx=Load()),
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conversion=-1),
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Constant(value=') is '),
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FormattedValue(
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value=Call(
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func=Name(id='sin', ctx=Load()),
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args=[
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Name(id='a', ctx=Load())],
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keywords=[]),
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conversion=-1,
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format_spec=JoinedStr(
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values=[
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Constant(value='.3')]))]))
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.. class:: List(elts, ctx)
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Tuple(elts, ctx)
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A list or tuple. ``elts`` holds a list of nodes representing the elements.
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``ctx`` is :class:`Store` if the container is an assignment target (i.e.
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``(x,y)=something``), and :class:`Load` otherwise.
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.. doctest::
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>>> print(ast.dump(ast.parse('[1, 2, 3]', mode='eval'), indent=4))
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Expression(
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body=List(
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elts=[
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Constant(value=1),
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Constant(value=2),
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Constant(value=3)],
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ctx=Load()))
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>>> print(ast.dump(ast.parse('(1, 2, 3)', mode='eval'), indent=4))
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Expression(
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body=Tuple(
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elts=[
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Constant(value=1),
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Constant(value=2),
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Constant(value=3)],
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ctx=Load()))
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.. class:: Set(elts)
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A set. ``elts`` holds a list of nodes representing the set's elements.
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.. doctest::
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>>> print(ast.dump(ast.parse('{1, 2, 3}', mode='eval'), indent=4))
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Expression(
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body=Set(
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elts=[
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Constant(value=1),
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Constant(value=2),
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Constant(value=3)]))
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.. class:: Dict(keys, values)
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A dictionary. ``keys`` and ``values`` hold lists of nodes representing the
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keys and the values respectively, in matching order (what would be returned
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when calling :code:`dictionary.keys()` and :code:`dictionary.values()`).
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When doing dictionary unpacking using dictionary literals the expression to be
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expanded goes in the ``values`` list, with a ``None`` at the corresponding
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position in ``keys``.
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.. doctest::
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>>> print(ast.dump(ast.parse('{"a":1, **d}', mode='eval'), indent=4))
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Expression(
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body=Dict(
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keys=[
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Constant(value='a'),
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None],
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values=[
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Constant(value=1),
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Name(id='d', ctx=Load())]))
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Variables
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^^^^^^^^^
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.. class:: Name(id, ctx)
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A variable name. ``id`` holds the name as a string, and ``ctx`` is one of
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the following types.
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.. class:: Load()
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Store()
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Del()
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Variable references can be used to load the value of a variable, to assign
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a new value to it, or to delete it. Variable references are given a context
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to distinguish these cases.
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.. doctest::
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>>> print(ast.dump(ast.parse('a'), indent=4))
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Module(
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body=[
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Expr(
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value=Name(id='a', ctx=Load()))],
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type_ignores=[])
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>>> print(ast.dump(ast.parse('a = 1'), indent=4))
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Module(
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body=[
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Assign(
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targets=[
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Name(id='a', ctx=Store())],
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value=Constant(value=1))],
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type_ignores=[])
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>>> print(ast.dump(ast.parse('del a'), indent=4))
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Module(
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body=[
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Delete(
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targets=[
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Name(id='a', ctx=Del())])],
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type_ignores=[])
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.. class:: Starred(value, ctx)
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A ``*var`` variable reference. ``value`` holds the variable, typically a
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:class:`Name` node. This type must be used when building a :class:`Call`
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node with ``*args``.
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.. doctest::
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>>> print(ast.dump(ast.parse('a, *b = it'), indent=4))
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Module(
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body=[
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Assign(
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targets=[
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Tuple(
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elts=[
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Name(id='a', ctx=Store()),
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Starred(
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value=Name(id='b', ctx=Store()),
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ctx=Store())],
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ctx=Store())],
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value=Name(id='it', ctx=Load()))],
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type_ignores=[])
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Expressions
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^^^^^^^^^^^
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.. class:: Expr(value)
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When an expression, such as a function call, appears as a statement by itself
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with its return value not used or stored, it is wrapped in this container.
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``value`` holds one of the other nodes in this section, a :class:`Constant`, a
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:class:`Name`, a :class:`Lambda`, a :class:`Yield` or :class:`YieldFrom` node.
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.. doctest::
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>>> print(ast.dump(ast.parse('-a'), indent=4))
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Module(
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body=[
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Expr(
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value=UnaryOp(
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op=USub(),
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operand=Name(id='a', ctx=Load())))],
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type_ignores=[])
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.. class:: UnaryOp(op, operand)
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A unary operation. ``op`` is the operator, and ``operand`` any expression
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node.
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.. class:: UAdd
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USub
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Not
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Invert
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Unary operator tokens. :class:`Not` is the ``not`` keyword, :class:`Invert`
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is the ``~`` operator.
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.. doctest::
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>>> print(ast.dump(ast.parse('not x', mode='eval'), indent=4))
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Expression(
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body=UnaryOp(
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op=Not(),
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operand=Name(id='x', ctx=Load())))
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.. class:: BinOp(left, op, right)
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A binary operation (like addition or division). ``op`` is the operator, and
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``left`` and ``right`` are any expression nodes.
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.. doctest::
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>>> print(ast.dump(ast.parse('x + y', mode='eval'), indent=4))
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Expression(
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body=BinOp(
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left=Name(id='x', ctx=Load()),
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op=Add(),
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right=Name(id='y', ctx=Load())))
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.. class:: Add
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Sub
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Mult
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Div
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FloorDiv
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Mod
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Pow
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LShift
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RShift
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BitOr
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BitXor
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BitAnd
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MatMult
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Binary operator tokens.
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.. class:: BoolOp(op, values)
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A boolean operation, 'or' or 'and'. ``op`` is :class:`Or` or :class:`And`.
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``values`` are the values involved. Consecutive operations with the same
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operator, such as ``a or b or c``, are collapsed into one node with several
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values.
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This doesn't include ``not``, which is a :class:`UnaryOp`.
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.. doctest::
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>>> print(ast.dump(ast.parse('x or y', mode='eval'), indent=4))
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Expression(
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body=BoolOp(
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op=Or(),
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values=[
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Name(id='x', ctx=Load()),
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Name(id='y', ctx=Load())]))
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.. class:: And
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Or
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Boolean operator tokens.
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.. class:: Compare(left, ops, comparators)
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A comparison of two or more values. ``left`` is the first value in the
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comparison, ``ops`` the list of operators, and ``comparators`` the list
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of values after the first element in the comparison.
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.. doctest::
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>>> print(ast.dump(ast.parse('1 <= a < 10', mode='eval'), indent=4))
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Expression(
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body=Compare(
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left=Constant(value=1),
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ops=[
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LtE(),
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Lt()],
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comparators=[
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Name(id='a', ctx=Load()),
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Constant(value=10)]))
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.. class:: Eq
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NotEq
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Lt
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LtE
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Gt
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GtE
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Is
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IsNot
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In
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NotIn
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Comparison operator tokens.
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.. class:: Call(func, args, keywords, starargs, kwargs)
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A function call. ``func`` is the function, which will often be a
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:class:`Name` or :class:`Attribute` object. Of the arguments:
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* ``args`` holds a list of the arguments passed by position.
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* ``keywords`` holds a list of :class:`keyword` objects representing
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arguments passed by keyword.
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When creating a ``Call`` node, ``args`` and ``keywords`` are required, but
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they can be empty lists. ``starargs`` and ``kwargs`` are optional.
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.. doctest::
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>>> print(ast.dump(ast.parse('func(a, b=c, *d, **e)', mode='eval'), indent=4))
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Expression(
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body=Call(
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func=Name(id='func', ctx=Load()),
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args=[
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Name(id='a', ctx=Load()),
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Starred(
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value=Name(id='d', ctx=Load()),
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ctx=Load())],
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keywords=[
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keyword(
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arg='b',
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value=Name(id='c', ctx=Load())),
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keyword(
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value=Name(id='e', ctx=Load()))]))
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.. class:: keyword(arg, value)
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A keyword argument to a function call or class definition. ``arg`` is a raw
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string of the parameter name, ``value`` is a node to pass in.
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.. class:: IfExp(test, body, orelse)
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An expression such as ``a if b else c``. Each field holds a single node, so
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in the following example, all three are :class:`Name` nodes.
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.. doctest::
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>>> print(ast.dump(ast.parse('a if b else c', mode='eval'), indent=4))
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Expression(
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body=IfExp(
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test=Name(id='b', ctx=Load()),
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body=Name(id='a', ctx=Load()),
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orelse=Name(id='c', ctx=Load())))
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.. class:: Attribute(value, attr, ctx)
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Attribute access, e.g. ``d.keys``. ``value`` is a node, typically a
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:class:`Name`. ``attr`` is a bare string giving the name of the attribute,
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and ``ctx`` is :class:`Load`, :class:`Store` or :class:`Del` according to how
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the attribute is acted on.
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.. doctest::
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>>> print(ast.dump(ast.parse('snake.colour', mode='eval'), indent=4))
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Expression(
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body=Attribute(
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value=Name(id='snake', ctx=Load()),
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attr='colour',
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ctx=Load()))
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.. class:: NamedExpr(target, value)
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A named expression. This AST node is produced by the assignment expressions
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operator (also known as the walrus operator). As opposed to the :class:`Assign`
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node in which the first argument can be multiple nodes, in this case both
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``target`` and ``value`` must be single nodes.
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.. doctest::
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>>> print(ast.dump(ast.parse('(x := 4)', mode='eval'), indent=4))
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Expression(
|
|
body=NamedExpr(
|
|
target=Name(id='x', ctx=Store()),
|
|
value=Constant(value=4)))
|
|
|
|
|
|
Subscripting
|
|
~~~~~~~~~~~~
|
|
|
|
.. class:: Subscript(value, slice, ctx)
|
|
|
|
A subscript, such as ``l[1]``. ``value`` is the subscripted object
|
|
(usually sequence or mapping). ``slice`` is an index, slice or key.
|
|
It can be a :class:`Tuple` and contain a :class:`Slice`.
|
|
``ctx`` is :class:`Load`, :class:`Store` or :class:`Del`
|
|
according to the action performed with the subscript.
|
|
|
|
.. doctest::
|
|
|
|
>>> print(ast.dump(ast.parse('l[1:2, 3]', mode='eval'), indent=4))
|
|
Expression(
|
|
body=Subscript(
|
|
value=Name(id='l', ctx=Load()),
|
|
slice=Tuple(
|
|
elts=[
|
|
Slice(
|
|
lower=Constant(value=1),
|
|
upper=Constant(value=2)),
|
|
Constant(value=3)],
|
|
ctx=Load()),
|
|
ctx=Load()))
|
|
|
|
|
|
.. class:: Slice(lower, upper, step)
|
|
|
|
Regular slicing (on the form ``lower:upper`` or ``lower:upper:step``).
|
|
Can occur only inside the *slice* field of :class:`Subscript`, either
|
|
directly or as an element of :class:`Tuple`.
|
|
|
|
.. doctest::
|
|
|
|
>>> print(ast.dump(ast.parse('l[1:2]', mode='eval'), indent=4))
|
|
Expression(
|
|
body=Subscript(
|
|
value=Name(id='l', ctx=Load()),
|
|
slice=Slice(
|
|
lower=Constant(value=1),
|
|
upper=Constant(value=2)),
|
|
ctx=Load()))
|
|
|
|
|
|
Comprehensions
|
|
~~~~~~~~~~~~~~
|
|
|
|
.. class:: ListComp(elt, generators)
|
|
SetComp(elt, generators)
|
|
GeneratorExp(elt, generators)
|
|
DictComp(key, value, generators)
|
|
|
|
List and set comprehensions, generator expressions, and dictionary
|
|
comprehensions. ``elt`` (or ``key`` and ``value``) is a single node
|
|
representing the part that will be evaluated for each item.
|
|
|
|
``generators`` is a list of :class:`comprehension` nodes.
|
|
|
|
.. doctest::
|
|
|
|
>>> print(ast.dump(ast.parse('[x for x in numbers]', mode='eval'), indent=4))
|
|
Expression(
|
|
body=ListComp(
|
|
elt=Name(id='x', ctx=Load()),
|
|
generators=[
|
|
comprehension(
|
|
target=Name(id='x', ctx=Store()),
|
|
iter=Name(id='numbers', ctx=Load()),
|
|
ifs=[],
|
|
is_async=0)]))
|
|
>>> print(ast.dump(ast.parse('{x: x**2 for x in numbers}', mode='eval'), indent=4))
|
|
Expression(
|
|
body=DictComp(
|
|
key=Name(id='x', ctx=Load()),
|
|
value=BinOp(
|
|
left=Name(id='x', ctx=Load()),
|
|
op=Pow(),
|
|
right=Constant(value=2)),
|
|
generators=[
|
|
comprehension(
|
|
target=Name(id='x', ctx=Store()),
|
|
iter=Name(id='numbers', ctx=Load()),
|
|
ifs=[],
|
|
is_async=0)]))
|
|
>>> print(ast.dump(ast.parse('{x for x in numbers}', mode='eval'), indent=4))
|
|
Expression(
|
|
body=SetComp(
|
|
elt=Name(id='x', ctx=Load()),
|
|
generators=[
|
|
comprehension(
|
|
target=Name(id='x', ctx=Store()),
|
|
iter=Name(id='numbers', ctx=Load()),
|
|
ifs=[],
|
|
is_async=0)]))
|
|
|
|
|
|
.. class:: comprehension(target, iter, ifs, is_async)
|
|
|
|
One ``for`` clause in a comprehension. ``target`` is the reference to use for
|
|
each element - typically a :class:`Name` or :class:`Tuple` node. ``iter``
|
|
is the object to iterate over. ``ifs`` is a list of test expressions: each
|
|
``for`` clause can have multiple ``ifs``.
|
|
|
|
``is_async`` indicates a comprehension is asynchronous (using an
|
|
``async for`` instead of ``for``). The value is an integer (0 or 1).
|
|
|
|
.. doctest::
|
|
|
|
>>> print(ast.dump(ast.parse('[ord(c) for line in file for c in line]', mode='eval'),
|
|
... indent=4)) # Multiple comprehensions in one.
|
|
Expression(
|
|
body=ListComp(
|
|
elt=Call(
|
|
func=Name(id='ord', ctx=Load()),
|
|
args=[
|
|
Name(id='c', ctx=Load())],
|
|
keywords=[]),
|
|
generators=[
|
|
comprehension(
|
|
target=Name(id='line', ctx=Store()),
|
|
iter=Name(id='file', ctx=Load()),
|
|
ifs=[],
|
|
is_async=0),
|
|
comprehension(
|
|
target=Name(id='c', ctx=Store()),
|
|
iter=Name(id='line', ctx=Load()),
|
|
ifs=[],
|
|
is_async=0)]))
|
|
|
|
>>> print(ast.dump(ast.parse('(n**2 for n in it if n>5 if n<10)', mode='eval'),
|
|
... indent=4)) # generator comprehension
|
|
Expression(
|
|
body=GeneratorExp(
|
|
elt=BinOp(
|
|
left=Name(id='n', ctx=Load()),
|
|
op=Pow(),
|
|
right=Constant(value=2)),
|
|
generators=[
|
|
comprehension(
|
|
target=Name(id='n', ctx=Store()),
|
|
iter=Name(id='it', ctx=Load()),
|
|
ifs=[
|
|
Compare(
|
|
left=Name(id='n', ctx=Load()),
|
|
ops=[
|
|
Gt()],
|
|
comparators=[
|
|
Constant(value=5)]),
|
|
Compare(
|
|
left=Name(id='n', ctx=Load()),
|
|
ops=[
|
|
Lt()],
|
|
comparators=[
|
|
Constant(value=10)])],
|
|
is_async=0)]))
|
|
|
|
>>> print(ast.dump(ast.parse('[i async for i in soc]', mode='eval'),
|
|
... indent=4)) # Async comprehension
|
|
Expression(
|
|
body=ListComp(
|
|
elt=Name(id='i', ctx=Load()),
|
|
generators=[
|
|
comprehension(
|
|
target=Name(id='i', ctx=Store()),
|
|
iter=Name(id='soc', ctx=Load()),
|
|
ifs=[],
|
|
is_async=1)]))
|
|
|
|
Statements
|
|
^^^^^^^^^^
|
|
|
|
.. class:: Assign(targets, value, type_comment)
|
|
|
|
An assignment. ``targets`` is a list of nodes, and ``value`` is a single node.
|
|
|
|
Multiple nodes in ``targets`` represents assigning the same value to each.
|
|
Unpacking is represented by putting a :class:`Tuple` or :class:`List`
|
|
within ``targets``.
|
|
|
|
.. attribute:: type_comment
|
|
|
|
``type_comment`` is an optional string with the type annotation as a comment.
|
|
|
|
.. doctest::
|
|
|
|
>>> print(ast.dump(ast.parse('a = b = 1'), indent=4)) # Multiple assignment
|
|
Module(
|
|
body=[
|
|
Assign(
|
|
targets=[
|
|
Name(id='a', ctx=Store()),
|
|
Name(id='b', ctx=Store())],
|
|
value=Constant(value=1))],
|
|
type_ignores=[])
|
|
|
|
>>> print(ast.dump(ast.parse('a,b = c'), indent=4)) # Unpacking
|
|
Module(
|
|
body=[
|
|
Assign(
|
|
targets=[
|
|
Tuple(
|
|
elts=[
|
|
Name(id='a', ctx=Store()),
|
|
Name(id='b', ctx=Store())],
|
|
ctx=Store())],
|
|
value=Name(id='c', ctx=Load()))],
|
|
type_ignores=[])
|
|
|
|
|
|
.. class:: AnnAssign(target, annotation, value, simple)
|
|
|
|
An assignment with a type annotation. ``target`` is a single node and can
|
|
be a :class:`Name`, a :class:`Attribute` or a :class:`Subscript`.
|
|
``annotation`` is the annotation, such as a :class:`Constant` or :class:`Name`
|
|
node. ``value`` is a single optional node. ``simple`` is a boolean integer
|
|
set to True for a :class:`Name` node in ``target`` that do not appear in
|
|
between parenthesis and are hence pure names and not expressions.
|
|
|
|
.. doctest::
|
|
|
|
>>> print(ast.dump(ast.parse('c: int'), indent=4))
|
|
Module(
|
|
body=[
|
|
AnnAssign(
|
|
target=Name(id='c', ctx=Store()),
|
|
annotation=Name(id='int', ctx=Load()),
|
|
simple=1)],
|
|
type_ignores=[])
|
|
|
|
>>> print(ast.dump(ast.parse('(a): int = 1'), indent=4)) # Annotation with parenthesis
|
|
Module(
|
|
body=[
|
|
AnnAssign(
|
|
target=Name(id='a', ctx=Store()),
|
|
annotation=Name(id='int', ctx=Load()),
|
|
value=Constant(value=1),
|
|
simple=0)],
|
|
type_ignores=[])
|
|
|
|
>>> print(ast.dump(ast.parse('a.b: int'), indent=4)) # Attribute annotation
|
|
Module(
|
|
body=[
|
|
AnnAssign(
|
|
target=Attribute(
|
|
value=Name(id='a', ctx=Load()),
|
|
attr='b',
|
|
ctx=Store()),
|
|
annotation=Name(id='int', ctx=Load()),
|
|
simple=0)],
|
|
type_ignores=[])
|
|
|
|
>>> print(ast.dump(ast.parse('a[1]: int'), indent=4)) # Subscript annotation
|
|
Module(
|
|
body=[
|
|
AnnAssign(
|
|
target=Subscript(
|
|
value=Name(id='a', ctx=Load()),
|
|
slice=Constant(value=1),
|
|
ctx=Store()),
|
|
annotation=Name(id='int', ctx=Load()),
|
|
simple=0)],
|
|
type_ignores=[])
|
|
|
|
|
|
.. class:: AugAssign(target, op, value)
|
|
|
|
Augmented assignment, such as ``a += 1``. In the following example,
|
|
``target`` is a :class:`Name` node for ``x`` (with the :class:`Store`
|
|
context), ``op`` is :class:`Add`, and ``value`` is a :class:`Constant` with
|
|
value for 1.
|
|
|
|
The ``target`` attribute cannot be of class :class:`Tuple` or :class:`List`,
|
|
unlike the targets of :class:`Assign`.
|
|
|
|
.. doctest::
|
|
|
|
>>> print(ast.dump(ast.parse('x += 2'), indent=4))
|
|
Module(
|
|
body=[
|
|
AugAssign(
|
|
target=Name(id='x', ctx=Store()),
|
|
op=Add(),
|
|
value=Constant(value=2))],
|
|
type_ignores=[])
|
|
|
|
|
|
.. class:: Raise(exc, cause)
|
|
|
|
A ``raise`` statement. ``exc`` is the exception object to be raised, normally a
|
|
:class:`Call` or :class:`Name`, or ``None`` for a standalone ``raise``.
|
|
``cause`` is the optional part for ``y`` in ``raise x from y``.
|
|
|
|
.. doctest::
|
|
|
|
>>> print(ast.dump(ast.parse('raise x from y'), indent=4))
|
|
Module(
|
|
body=[
|
|
Raise(
|
|
exc=Name(id='x', ctx=Load()),
|
|
cause=Name(id='y', ctx=Load()))],
|
|
type_ignores=[])
|
|
|
|
|
|
.. class:: Assert(test, msg)
|
|
|
|
An assertion. ``test`` holds the condition, such as a :class:`Compare` node.
|
|
``msg`` holds the failure message.
|
|
|
|
.. doctest::
|
|
|
|
>>> print(ast.dump(ast.parse('assert x,y'), indent=4))
|
|
Module(
|
|
body=[
|
|
Assert(
|
|
test=Name(id='x', ctx=Load()),
|
|
msg=Name(id='y', ctx=Load()))],
|
|
type_ignores=[])
|
|
|
|
|
|
.. class:: Delete(targets)
|
|
|
|
Represents a ``del`` statement. ``targets`` is a list of nodes, such as
|
|
:class:`Name`, :class:`Attribute` or :class:`Subscript` nodes.
|
|
|
|
.. doctest::
|
|
|
|
>>> print(ast.dump(ast.parse('del x,y,z'), indent=4))
|
|
Module(
|
|
body=[
|
|
Delete(
|
|
targets=[
|
|
Name(id='x', ctx=Del()),
|
|
Name(id='y', ctx=Del()),
|
|
Name(id='z', ctx=Del())])],
|
|
type_ignores=[])
|
|
|
|
|
|
.. class:: Pass()
|
|
|
|
A ``pass`` statement.
|
|
|
|
.. doctest::
|
|
|
|
>>> print(ast.dump(ast.parse('pass'), indent=4))
|
|
Module(
|
|
body=[
|
|
Pass()],
|
|
type_ignores=[])
|
|
|
|
|
|
Other statements which are only applicable inside functions or loops are
|
|
described in other sections.
|
|
|
|
Imports
|
|
~~~~~~~
|
|
|
|
.. class:: Import(names)
|
|
|
|
An import statement. ``names`` is a list of :class:`alias` nodes.
|
|
|
|
.. doctest::
|
|
|
|
>>> print(ast.dump(ast.parse('import x,y,z'), indent=4))
|
|
Module(
|
|
body=[
|
|
Import(
|
|
names=[
|
|
alias(name='x'),
|
|
alias(name='y'),
|
|
alias(name='z')])],
|
|
type_ignores=[])
|
|
|
|
|
|
.. class:: ImportFrom(module, names, level)
|
|
|
|
Represents ``from x import y``. ``module`` is a raw string of the 'from' name,
|
|
without any leading dots, or ``None`` for statements such as ``from . import foo``.
|
|
``level`` is an integer holding the level of the relative import (0 means
|
|
absolute import).
|
|
|
|
.. doctest::
|
|
|
|
>>> print(ast.dump(ast.parse('from y import x,y,z'), indent=4))
|
|
Module(
|
|
body=[
|
|
ImportFrom(
|
|
module='y',
|
|
names=[
|
|
alias(name='x'),
|
|
alias(name='y'),
|
|
alias(name='z')],
|
|
level=0)],
|
|
type_ignores=[])
|
|
|
|
|
|
.. class:: alias(name, asname)
|
|
|
|
Both parameters are raw strings of the names. ``asname`` can be ``None`` if
|
|
the regular name is to be used.
|
|
|
|
.. doctest::
|
|
|
|
>>> print(ast.dump(ast.parse('from ..foo.bar import a as b, c'), indent=4))
|
|
Module(
|
|
body=[
|
|
ImportFrom(
|
|
module='foo.bar',
|
|
names=[
|
|
alias(name='a', asname='b'),
|
|
alias(name='c')],
|
|
level=2)],
|
|
type_ignores=[])
|
|
|
|
Control flow
|
|
^^^^^^^^^^^^
|
|
|
|
.. note::
|
|
Optional clauses such as ``else`` are stored as an empty list if they're
|
|
not present.
|
|
|
|
.. class:: If(test, body, orelse)
|
|
|
|
An ``if`` statement. ``test`` holds a single node, such as a :class:`Compare`
|
|
node. ``body`` and ``orelse`` each hold a list of nodes.
|
|
|
|
``elif`` clauses don't have a special representation in the AST, but rather
|
|
appear as extra :class:`If` nodes within the ``orelse`` section of the
|
|
previous one.
|
|
|
|
.. doctest::
|
|
|
|
>>> print(ast.dump(ast.parse("""
|
|
... if x:
|
|
... ...
|
|
... elif y:
|
|
... ...
|
|
... else:
|
|
... ...
|
|
... """), indent=4))
|
|
Module(
|
|
body=[
|
|
If(
|
|
test=Name(id='x', ctx=Load()),
|
|
body=[
|
|
Expr(
|
|
value=Constant(value=Ellipsis))],
|
|
orelse=[
|
|
If(
|
|
test=Name(id='y', ctx=Load()),
|
|
body=[
|
|
Expr(
|
|
value=Constant(value=Ellipsis))],
|
|
orelse=[
|
|
Expr(
|
|
value=Constant(value=Ellipsis))])])],
|
|
type_ignores=[])
|
|
|
|
|
|
.. class:: For(target, iter, body, orelse, type_comment)
|
|
|
|
A ``for`` loop. ``target`` holds the variable(s) the loop assigns to, as a
|
|
single :class:`Name`, :class:`Tuple` or :class:`List` node. ``iter`` holds
|
|
the item to be looped over, again as a single node. ``body`` and ``orelse``
|
|
contain lists of nodes to execute. Those in ``orelse`` are executed if the
|
|
loop finishes normally, rather than via a ``break`` statement.
|
|
|
|
.. attribute:: type_comment
|
|
|
|
``type_comment`` is an optional string with the type annotation as a comment.
|
|
|
|
.. doctest::
|
|
|
|
>>> print(ast.dump(ast.parse("""
|
|
... for x in y:
|
|
... ...
|
|
... else:
|
|
... ...
|
|
... """), indent=4))
|
|
Module(
|
|
body=[
|
|
For(
|
|
target=Name(id='x', ctx=Store()),
|
|
iter=Name(id='y', ctx=Load()),
|
|
body=[
|
|
Expr(
|
|
value=Constant(value=Ellipsis))],
|
|
orelse=[
|
|
Expr(
|
|
value=Constant(value=Ellipsis))])],
|
|
type_ignores=[])
|
|
|
|
|
|
.. class:: While(test, body, orelse)
|
|
|
|
A ``while`` loop. ``test`` holds the condition, such as a :class:`Compare`
|
|
node.
|
|
|
|
.. doctest::
|
|
|
|
>> print(ast.dump(ast.parse("""
|
|
... while x:
|
|
... ...
|
|
... else:
|
|
... ...
|
|
... """), indent=4))
|
|
Module(
|
|
body=[
|
|
While(
|
|
test=Name(id='x', ctx=Load()),
|
|
body=[
|
|
Expr(
|
|
value=Constant(value=Ellipsis))],
|
|
orelse=[
|
|
Expr(
|
|
value=Constant(value=Ellipsis))])],
|
|
type_ignores=[])
|
|
|
|
|
|
.. class:: Break
|
|
Continue
|
|
|
|
The ``break`` and ``continue`` statements.
|
|
|
|
.. doctest::
|
|
|
|
>>> print(ast.dump(ast.parse("""\
|
|
... for a in b:
|
|
... if a > 5:
|
|
... break
|
|
... else:
|
|
... continue
|
|
...
|
|
... """), indent=4))
|
|
Module(
|
|
body=[
|
|
For(
|
|
target=Name(id='a', ctx=Store()),
|
|
iter=Name(id='b', ctx=Load()),
|
|
body=[
|
|
If(
|
|
test=Compare(
|
|
left=Name(id='a', ctx=Load()),
|
|
ops=[
|
|
Gt()],
|
|
comparators=[
|
|
Constant(value=5)]),
|
|
body=[
|
|
Break()],
|
|
orelse=[
|
|
Continue()])],
|
|
orelse=[])],
|
|
type_ignores=[])
|
|
|
|
|
|
.. class:: Try(body, handlers, orelse, finalbody)
|
|
|
|
``try`` blocks. All attributes are list of nodes to execute, except for
|
|
``handlers``, which is a list of :class:`ExceptHandler` nodes.
|
|
|
|
.. doctest::
|
|
|
|
>>> print(ast.dump(ast.parse("""
|
|
... try:
|
|
... ...
|
|
... except Exception:
|
|
... ...
|
|
... except OtherException as e:
|
|
... ...
|
|
... else:
|
|
... ...
|
|
... finally:
|
|
... ...
|
|
... """), indent=4))
|
|
Module(
|
|
body=[
|
|
Try(
|
|
body=[
|
|
Expr(
|
|
value=Constant(value=Ellipsis))],
|
|
handlers=[
|
|
ExceptHandler(
|
|
type=Name(id='Exception', ctx=Load()),
|
|
body=[
|
|
Expr(
|
|
value=Constant(value=Ellipsis))]),
|
|
ExceptHandler(
|
|
type=Name(id='OtherException', ctx=Load()),
|
|
name='e',
|
|
body=[
|
|
Expr(
|
|
value=Constant(value=Ellipsis))])],
|
|
orelse=[
|
|
Expr(
|
|
value=Constant(value=Ellipsis))],
|
|
finalbody=[
|
|
Expr(
|
|
value=Constant(value=Ellipsis))])],
|
|
type_ignores=[])
|
|
|
|
|
|
.. class:: TryStar(body, handlers, orelse, finalbody)
|
|
|
|
``try`` blocks which are followed by ``except*`` clauses. The attributes are the
|
|
same as for :class:`Try` but the :class:`ExceptHandler` nodes in ``handlers``
|
|
are interpreted as ``except*`` blocks rather then ``except``.
|
|
|
|
.. doctest::
|
|
|
|
>>> print(ast.dump(ast.parse("""
|
|
... try:
|
|
... ...
|
|
... except* Exception:
|
|
... ...
|
|
... """), indent=4))
|
|
Module(
|
|
body=[
|
|
TryStar(
|
|
body=[
|
|
Expr(
|
|
value=Constant(value=Ellipsis))],
|
|
handlers=[
|
|
ExceptHandler(
|
|
type=Name(id='Exception', ctx=Load()),
|
|
body=[
|
|
Expr(
|
|
value=Constant(value=Ellipsis))])],
|
|
orelse=[],
|
|
finalbody=[])],
|
|
type_ignores=[])
|
|
|
|
|
|
.. class:: ExceptHandler(type, name, body)
|
|
|
|
A single ``except`` clause. ``type`` is the exception type it will match,
|
|
typically a :class:`Name` node (or ``None`` for a catch-all ``except:`` clause).
|
|
``name`` is a raw string for the name to hold the exception, or ``None`` if
|
|
the clause doesn't have ``as foo``. ``body`` is a list of nodes.
|
|
|
|
.. doctest::
|
|
|
|
>>> print(ast.dump(ast.parse("""\
|
|
... try:
|
|
... a + 1
|
|
... except TypeError:
|
|
... pass
|
|
... """), indent=4))
|
|
Module(
|
|
body=[
|
|
Try(
|
|
body=[
|
|
Expr(
|
|
value=BinOp(
|
|
left=Name(id='a', ctx=Load()),
|
|
op=Add(),
|
|
right=Constant(value=1)))],
|
|
handlers=[
|
|
ExceptHandler(
|
|
type=Name(id='TypeError', ctx=Load()),
|
|
body=[
|
|
Pass()])],
|
|
orelse=[],
|
|
finalbody=[])],
|
|
type_ignores=[])
|
|
|
|
|
|
.. class:: With(items, body, type_comment)
|
|
|
|
A ``with`` block. ``items`` is a list of :class:`withitem` nodes representing
|
|
the context managers, and ``body`` is the indented block inside the context.
|
|
|
|
.. attribute:: type_comment
|
|
|
|
``type_comment`` is an optional string with the type annotation as a comment.
|
|
|
|
|
|
.. class:: withitem(context_expr, optional_vars)
|
|
|
|
A single context manager in a ``with`` block. ``context_expr`` is the context
|
|
manager, often a :class:`Call` node. ``optional_vars`` is a :class:`Name`,
|
|
:class:`Tuple` or :class:`List` for the ``as foo`` part, or ``None`` if that
|
|
isn't used.
|
|
|
|
.. doctest::
|
|
|
|
>>> print(ast.dump(ast.parse("""\
|
|
... with a as b, c as d:
|
|
... something(b, d)
|
|
... """), indent=4))
|
|
Module(
|
|
body=[
|
|
With(
|
|
items=[
|
|
withitem(
|
|
context_expr=Name(id='a', ctx=Load()),
|
|
optional_vars=Name(id='b', ctx=Store())),
|
|
withitem(
|
|
context_expr=Name(id='c', ctx=Load()),
|
|
optional_vars=Name(id='d', ctx=Store()))],
|
|
body=[
|
|
Expr(
|
|
value=Call(
|
|
func=Name(id='something', ctx=Load()),
|
|
args=[
|
|
Name(id='b', ctx=Load()),
|
|
Name(id='d', ctx=Load())],
|
|
keywords=[]))])],
|
|
type_ignores=[])
|
|
|
|
|
|
Pattern matching
|
|
^^^^^^^^^^^^^^^^
|
|
|
|
|
|
.. class:: Match(subject, cases)
|
|
|
|
A ``match`` statement. ``subject`` holds the subject of the match (the object
|
|
that is being matched against the cases) and ``cases`` contains an iterable of
|
|
:class:`match_case` nodes with the different cases.
|
|
|
|
.. class:: match_case(pattern, guard, body)
|
|
|
|
A single case pattern in a ``match`` statement. ``pattern`` contains the
|
|
match pattern that the subject will be matched against. Note that the
|
|
:class:`AST` nodes produced for patterns differ from those produced for
|
|
expressions, even when they share the same syntax.
|
|
|
|
The ``guard`` attribute contains an expression that will be evaluated if
|
|
the pattern matches the subject.
|
|
|
|
``body`` contains a list of nodes to execute if the pattern matches and
|
|
the result of evaluating the guard expression is true.
|
|
|
|
.. doctest::
|
|
|
|
>>> print(ast.dump(ast.parse("""
|
|
... match x:
|
|
... case [x] if x>0:
|
|
... ...
|
|
... case tuple():
|
|
... ...
|
|
... """), indent=4))
|
|
Module(
|
|
body=[
|
|
Match(
|
|
subject=Name(id='x', ctx=Load()),
|
|
cases=[
|
|
match_case(
|
|
pattern=MatchSequence(
|
|
patterns=[
|
|
MatchAs(name='x')]),
|
|
guard=Compare(
|
|
left=Name(id='x', ctx=Load()),
|
|
ops=[
|
|
Gt()],
|
|
comparators=[
|
|
Constant(value=0)]),
|
|
body=[
|
|
Expr(
|
|
value=Constant(value=Ellipsis))]),
|
|
match_case(
|
|
pattern=MatchClass(
|
|
cls=Name(id='tuple', ctx=Load()),
|
|
patterns=[],
|
|
kwd_attrs=[],
|
|
kwd_patterns=[]),
|
|
body=[
|
|
Expr(
|
|
value=Constant(value=Ellipsis))])])],
|
|
type_ignores=[])
|
|
|
|
.. class:: MatchValue(value)
|
|
|
|
A match literal or value pattern that compares by equality. ``value`` is
|
|
an expression node. Permitted value nodes are restricted as described in
|
|
the match statement documentation. This pattern succeeds if the match
|
|
subject is equal to the evaluated value.
|
|
|
|
.. doctest::
|
|
|
|
>>> print(ast.dump(ast.parse("""
|
|
... match x:
|
|
... case "Relevant":
|
|
... ...
|
|
... """), indent=4))
|
|
Module(
|
|
body=[
|
|
Match(
|
|
subject=Name(id='x', ctx=Load()),
|
|
cases=[
|
|
match_case(
|
|
pattern=MatchValue(
|
|
value=Constant(value='Relevant')),
|
|
body=[
|
|
Expr(
|
|
value=Constant(value=Ellipsis))])])],
|
|
type_ignores=[])
|
|
|
|
.. class:: MatchSingleton(value)
|
|
|
|
A match literal pattern that compares by identity. ``value`` is the
|
|
singleton to be compared against: ``None``, ``True``, or ``False``. This
|
|
pattern succeeds if the match subject is the given constant.
|
|
|
|
.. doctest::
|
|
|
|
>>> print(ast.dump(ast.parse("""
|
|
... match x:
|
|
... case None:
|
|
... ...
|
|
... """), indent=4))
|
|
Module(
|
|
body=[
|
|
Match(
|
|
subject=Name(id='x', ctx=Load()),
|
|
cases=[
|
|
match_case(
|
|
pattern=MatchSingleton(value=None),
|
|
body=[
|
|
Expr(
|
|
value=Constant(value=Ellipsis))])])],
|
|
type_ignores=[])
|
|
|
|
.. class:: MatchSequence(patterns)
|
|
|
|
A match sequence pattern. ``patterns`` contains the patterns to be matched
|
|
against the subject elements if the subject is a sequence. Matches a variable
|
|
length sequence if one of the subpatterns is a ``MatchStar`` node, otherwise
|
|
matches a fixed length sequence.
|
|
|
|
.. doctest::
|
|
|
|
>>> print(ast.dump(ast.parse("""
|
|
... match x:
|
|
... case [1, 2]:
|
|
... ...
|
|
... """), indent=4))
|
|
Module(
|
|
body=[
|
|
Match(
|
|
subject=Name(id='x', ctx=Load()),
|
|
cases=[
|
|
match_case(
|
|
pattern=MatchSequence(
|
|
patterns=[
|
|
MatchValue(
|
|
value=Constant(value=1)),
|
|
MatchValue(
|
|
value=Constant(value=2))]),
|
|
body=[
|
|
Expr(
|
|
value=Constant(value=Ellipsis))])])],
|
|
type_ignores=[])
|
|
|
|
.. class:: MatchStar(name)
|
|
|
|
Matches the rest of the sequence in a variable length match sequence pattern.
|
|
If ``name`` is not ``None``, a list containing the remaining sequence
|
|
elements is bound to that name if the overall sequence pattern is successful.
|
|
|
|
.. doctest::
|
|
|
|
>>> print(ast.dump(ast.parse("""
|
|
... match x:
|
|
... case [1, 2, *rest]:
|
|
... ...
|
|
... case [*_]:
|
|
... ...
|
|
... """), indent=4))
|
|
Module(
|
|
body=[
|
|
Match(
|
|
subject=Name(id='x', ctx=Load()),
|
|
cases=[
|
|
match_case(
|
|
pattern=MatchSequence(
|
|
patterns=[
|
|
MatchValue(
|
|
value=Constant(value=1)),
|
|
MatchValue(
|
|
value=Constant(value=2)),
|
|
MatchStar(name='rest')]),
|
|
body=[
|
|
Expr(
|
|
value=Constant(value=Ellipsis))]),
|
|
match_case(
|
|
pattern=MatchSequence(
|
|
patterns=[
|
|
MatchStar()]),
|
|
body=[
|
|
Expr(
|
|
value=Constant(value=Ellipsis))])])],
|
|
type_ignores=[])
|
|
|
|
.. class:: MatchMapping(keys, patterns, rest)
|
|
|
|
A match mapping pattern. ``keys`` is a sequence of expression nodes.
|
|
``patterns`` is a corresponding sequence of pattern nodes. ``rest`` is an
|
|
optional name that can be specified to capture the remaining mapping elements.
|
|
Permitted key expressions are restricted as described in the match statement
|
|
documentation.
|
|
|
|
This pattern succeeds if the subject is a mapping, all evaluated key
|
|
expressions are present in the mapping, and the value corresponding to each
|
|
key matches the corresponding subpattern. If ``rest`` is not ``None``, a dict
|
|
containing the remaining mapping elements is bound to that name if the overall
|
|
mapping pattern is successful.
|
|
|
|
.. doctest::
|
|
|
|
>>> print(ast.dump(ast.parse("""
|
|
... match x:
|
|
... case {1: _, 2: _}:
|
|
... ...
|
|
... case {**rest}:
|
|
... ...
|
|
... """), indent=4))
|
|
Module(
|
|
body=[
|
|
Match(
|
|
subject=Name(id='x', ctx=Load()),
|
|
cases=[
|
|
match_case(
|
|
pattern=MatchMapping(
|
|
keys=[
|
|
Constant(value=1),
|
|
Constant(value=2)],
|
|
patterns=[
|
|
MatchAs(),
|
|
MatchAs()]),
|
|
body=[
|
|
Expr(
|
|
value=Constant(value=Ellipsis))]),
|
|
match_case(
|
|
pattern=MatchMapping(keys=[], patterns=[], rest='rest'),
|
|
body=[
|
|
Expr(
|
|
value=Constant(value=Ellipsis))])])],
|
|
type_ignores=[])
|
|
|
|
.. class:: MatchClass(cls, patterns, kwd_attrs, kwd_patterns)
|
|
|
|
A match class pattern. ``cls`` is an expression giving the nominal class to
|
|
be matched. ``patterns`` is a sequence of pattern nodes to be matched against
|
|
the class defined sequence of pattern matching attributes. ``kwd_attrs`` is a
|
|
sequence of additional attributes to be matched (specified as keyword arguments
|
|
in the class pattern), ``kwd_patterns`` are the corresponding patterns
|
|
(specified as keyword values in the class pattern).
|
|
|
|
This pattern succeeds if the subject is an instance of the nominated class,
|
|
all positional patterns match the corresponding class-defined attributes, and
|
|
any specified keyword attributes match their corresponding pattern.
|
|
|
|
Note: classes may define a property that returns self in order to match a
|
|
pattern node against the instance being matched. Several builtin types are
|
|
also matched that way, as described in the match statement documentation.
|
|
|
|
.. doctest::
|
|
|
|
>>> print(ast.dump(ast.parse("""
|
|
... match x:
|
|
... case Point2D(0, 0):
|
|
... ...
|
|
... case Point3D(x=0, y=0, z=0):
|
|
... ...
|
|
... """), indent=4))
|
|
Module(
|
|
body=[
|
|
Match(
|
|
subject=Name(id='x', ctx=Load()),
|
|
cases=[
|
|
match_case(
|
|
pattern=MatchClass(
|
|
cls=Name(id='Point2D', ctx=Load()),
|
|
patterns=[
|
|
MatchValue(
|
|
value=Constant(value=0)),
|
|
MatchValue(
|
|
value=Constant(value=0))],
|
|
kwd_attrs=[],
|
|
kwd_patterns=[]),
|
|
body=[
|
|
Expr(
|
|
value=Constant(value=Ellipsis))]),
|
|
match_case(
|
|
pattern=MatchClass(
|
|
cls=Name(id='Point3D', ctx=Load()),
|
|
patterns=[],
|
|
kwd_attrs=[
|
|
'x',
|
|
'y',
|
|
'z'],
|
|
kwd_patterns=[
|
|
MatchValue(
|
|
value=Constant(value=0)),
|
|
MatchValue(
|
|
value=Constant(value=0)),
|
|
MatchValue(
|
|
value=Constant(value=0))]),
|
|
body=[
|
|
Expr(
|
|
value=Constant(value=Ellipsis))])])],
|
|
type_ignores=[])
|
|
|
|
.. class:: MatchAs(pattern, name)
|
|
|
|
A match "as-pattern", capture pattern or wildcard pattern. ``pattern``
|
|
contains the match pattern that the subject will be matched against.
|
|
If the pattern is ``None``, the node represents a capture pattern (i.e a
|
|
bare name) and will always succeed.
|
|
|
|
The ``name`` attribute contains the name that will be bound if the pattern
|
|
is successful. If ``name`` is ``None``, ``pattern`` must also be ``None``
|
|
and the node represents the wildcard pattern.
|
|
|
|
.. doctest::
|
|
|
|
>>> print(ast.dump(ast.parse("""
|
|
... match x:
|
|
... case [x] as y:
|
|
... ...
|
|
... case _:
|
|
... ...
|
|
... """), indent=4))
|
|
Module(
|
|
body=[
|
|
Match(
|
|
subject=Name(id='x', ctx=Load()),
|
|
cases=[
|
|
match_case(
|
|
pattern=MatchAs(
|
|
pattern=MatchSequence(
|
|
patterns=[
|
|
MatchAs(name='x')]),
|
|
name='y'),
|
|
body=[
|
|
Expr(
|
|
value=Constant(value=Ellipsis))]),
|
|
match_case(
|
|
pattern=MatchAs(),
|
|
body=[
|
|
Expr(
|
|
value=Constant(value=Ellipsis))])])],
|
|
type_ignores=[])
|
|
|
|
.. class:: MatchOr(patterns)
|
|
|
|
A match "or-pattern". An or-pattern matches each of its subpatterns in turn
|
|
to the subject, until one succeeds. The or-pattern is then deemed to
|
|
succeed. If none of the subpatterns succeed the or-pattern fails. The
|
|
``patterns`` attribute contains a list of match pattern nodes that will be
|
|
matched against the subject.
|
|
|
|
.. doctest::
|
|
|
|
>>> print(ast.dump(ast.parse("""
|
|
... match x:
|
|
... case [x] | (y):
|
|
... ...
|
|
... """), indent=4))
|
|
Module(
|
|
body=[
|
|
Match(
|
|
subject=Name(id='x', ctx=Load()),
|
|
cases=[
|
|
match_case(
|
|
pattern=MatchOr(
|
|
patterns=[
|
|
MatchSequence(
|
|
patterns=[
|
|
MatchAs(name='x')]),
|
|
MatchAs(name='y')]),
|
|
body=[
|
|
Expr(
|
|
value=Constant(value=Ellipsis))])])],
|
|
type_ignores=[])
|
|
|
|
|
|
Function and class definitions
|
|
^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
|
|
|
|
.. class:: FunctionDef(name, args, body, decorator_list, returns, type_comment)
|
|
|
|
A function definition.
|
|
|
|
* ``name`` is a raw string of the function name.
|
|
* ``args`` is an :class:`arguments` node.
|
|
* ``body`` is the list of nodes inside the function.
|
|
* ``decorator_list`` is the list of decorators to be applied, stored outermost
|
|
first (i.e. the first in the list will be applied last).
|
|
* ``returns`` is the return annotation.
|
|
|
|
.. attribute:: type_comment
|
|
|
|
``type_comment`` is an optional string with the type annotation as a comment.
|
|
|
|
|
|
.. class:: Lambda(args, body)
|
|
|
|
``lambda`` is a minimal function definition that can be used inside an
|
|
expression. Unlike :class:`FunctionDef`, ``body`` holds a single node.
|
|
|
|
.. doctest::
|
|
|
|
>>> print(ast.dump(ast.parse('lambda x,y: ...'), indent=4))
|
|
Module(
|
|
body=[
|
|
Expr(
|
|
value=Lambda(
|
|
args=arguments(
|
|
posonlyargs=[],
|
|
args=[
|
|
arg(arg='x'),
|
|
arg(arg='y')],
|
|
kwonlyargs=[],
|
|
kw_defaults=[],
|
|
defaults=[]),
|
|
body=Constant(value=Ellipsis)))],
|
|
type_ignores=[])
|
|
|
|
|
|
.. class:: arguments(posonlyargs, args, vararg, kwonlyargs, kw_defaults, kwarg, defaults)
|
|
|
|
The arguments for a function.
|
|
|
|
* ``posonlyargs``, ``args`` and ``kwonlyargs`` are lists of :class:`arg` nodes.
|
|
* ``vararg`` and ``kwarg`` are single :class:`arg` nodes, referring to the
|
|
``*args, **kwargs`` parameters.
|
|
* ``kw_defaults`` is a list of default values for keyword-only arguments. If
|
|
one is ``None``, the corresponding argument is required.
|
|
* ``defaults`` is a list of default values for arguments that can be passed
|
|
positionally. If there are fewer defaults, they correspond to the last n
|
|
arguments.
|
|
|
|
|
|
.. class:: arg(arg, annotation, type_comment)
|
|
|
|
A single argument in a list. ``arg`` is a raw string of the argument
|
|
name, ``annotation`` is its annotation, such as a :class:`Str` or
|
|
:class:`Name` node.
|
|
|
|
.. attribute:: type_comment
|
|
|
|
``type_comment`` is an optional string with the type annotation as a comment
|
|
|
|
.. doctest::
|
|
|
|
>>> print(ast.dump(ast.parse("""\
|
|
... @decorator1
|
|
... @decorator2
|
|
... def f(a: 'annotation', b=1, c=2, *d, e, f=3, **g) -> 'return annotation':
|
|
... pass
|
|
... """), indent=4))
|
|
Module(
|
|
body=[
|
|
FunctionDef(
|
|
name='f',
|
|
args=arguments(
|
|
posonlyargs=[],
|
|
args=[
|
|
arg(
|
|
arg='a',
|
|
annotation=Constant(value='annotation')),
|
|
arg(arg='b'),
|
|
arg(arg='c')],
|
|
vararg=arg(arg='d'),
|
|
kwonlyargs=[
|
|
arg(arg='e'),
|
|
arg(arg='f')],
|
|
kw_defaults=[
|
|
None,
|
|
Constant(value=3)],
|
|
kwarg=arg(arg='g'),
|
|
defaults=[
|
|
Constant(value=1),
|
|
Constant(value=2)]),
|
|
body=[
|
|
Pass()],
|
|
decorator_list=[
|
|
Name(id='decorator1', ctx=Load()),
|
|
Name(id='decorator2', ctx=Load())],
|
|
returns=Constant(value='return annotation'))],
|
|
type_ignores=[])
|
|
|
|
|
|
.. class:: Return(value)
|
|
|
|
A ``return`` statement.
|
|
|
|
.. doctest::
|
|
|
|
>>> print(ast.dump(ast.parse('return 4'), indent=4))
|
|
Module(
|
|
body=[
|
|
Return(
|
|
value=Constant(value=4))],
|
|
type_ignores=[])
|
|
|
|
|
|
.. class:: Yield(value)
|
|
YieldFrom(value)
|
|
|
|
A ``yield`` or ``yield from`` expression. Because these are expressions, they
|
|
must be wrapped in a :class:`Expr` node if the value sent back is not used.
|
|
|
|
.. doctest::
|
|
|
|
>>> print(ast.dump(ast.parse('yield x'), indent=4))
|
|
Module(
|
|
body=[
|
|
Expr(
|
|
value=Yield(
|
|
value=Name(id='x', ctx=Load())))],
|
|
type_ignores=[])
|
|
|
|
>>> print(ast.dump(ast.parse('yield from x'), indent=4))
|
|
Module(
|
|
body=[
|
|
Expr(
|
|
value=YieldFrom(
|
|
value=Name(id='x', ctx=Load())))],
|
|
type_ignores=[])
|
|
|
|
|
|
.. class:: Global(names)
|
|
Nonlocal(names)
|
|
|
|
``global`` and ``nonlocal`` statements. ``names`` is a list of raw strings.
|
|
|
|
.. doctest::
|
|
|
|
>>> print(ast.dump(ast.parse('global x,y,z'), indent=4))
|
|
Module(
|
|
body=[
|
|
Global(
|
|
names=[
|
|
'x',
|
|
'y',
|
|
'z'])],
|
|
type_ignores=[])
|
|
|
|
>>> print(ast.dump(ast.parse('nonlocal x,y,z'), indent=4))
|
|
Module(
|
|
body=[
|
|
Nonlocal(
|
|
names=[
|
|
'x',
|
|
'y',
|
|
'z'])],
|
|
type_ignores=[])
|
|
|
|
|
|
.. class:: ClassDef(name, bases, keywords, starargs, kwargs, body, decorator_list)
|
|
|
|
A class definition.
|
|
|
|
* ``name`` is a raw string for the class name
|
|
* ``bases`` is a list of nodes for explicitly specified base classes.
|
|
* ``keywords`` is a list of :class:`keyword` nodes, principally for 'metaclass'.
|
|
Other keywords will be passed to the metaclass, as per `PEP-3115
|
|
<https://peps.python.org/pep-3115/>`_.
|
|
* ``starargs`` and ``kwargs`` are each a single node, as in a function call.
|
|
starargs will be expanded to join the list of base classes, and kwargs will
|
|
be passed to the metaclass.
|
|
* ``body`` is a list of nodes representing the code within the class
|
|
definition.
|
|
* ``decorator_list`` is a list of nodes, as in :class:`FunctionDef`.
|
|
|
|
.. doctest::
|
|
|
|
>>> print(ast.dump(ast.parse("""\
|
|
... @decorator1
|
|
... @decorator2
|
|
... class Foo(base1, base2, metaclass=meta):
|
|
... pass
|
|
... """), indent=4))
|
|
Module(
|
|
body=[
|
|
ClassDef(
|
|
name='Foo',
|
|
bases=[
|
|
Name(id='base1', ctx=Load()),
|
|
Name(id='base2', ctx=Load())],
|
|
keywords=[
|
|
keyword(
|
|
arg='metaclass',
|
|
value=Name(id='meta', ctx=Load()))],
|
|
body=[
|
|
Pass()],
|
|
decorator_list=[
|
|
Name(id='decorator1', ctx=Load()),
|
|
Name(id='decorator2', ctx=Load())])],
|
|
type_ignores=[])
|
|
|
|
Async and await
|
|
^^^^^^^^^^^^^^^
|
|
|
|
.. class:: AsyncFunctionDef(name, args, body, decorator_list, returns, type_comment)
|
|
|
|
An ``async def`` function definition. Has the same fields as
|
|
:class:`FunctionDef`.
|
|
|
|
|
|
.. class:: Await(value)
|
|
|
|
An ``await`` expression. ``value`` is what it waits for.
|
|
Only valid in the body of an :class:`AsyncFunctionDef`.
|
|
|
|
.. doctest::
|
|
|
|
>>> print(ast.dump(ast.parse("""\
|
|
... async def f():
|
|
... await other_func()
|
|
... """), indent=4))
|
|
Module(
|
|
body=[
|
|
AsyncFunctionDef(
|
|
name='f',
|
|
args=arguments(
|
|
posonlyargs=[],
|
|
args=[],
|
|
kwonlyargs=[],
|
|
kw_defaults=[],
|
|
defaults=[]),
|
|
body=[
|
|
Expr(
|
|
value=Await(
|
|
value=Call(
|
|
func=Name(id='other_func', ctx=Load()),
|
|
args=[],
|
|
keywords=[])))],
|
|
decorator_list=[])],
|
|
type_ignores=[])
|
|
|
|
|
|
.. class:: AsyncFor(target, iter, body, orelse, type_comment)
|
|
AsyncWith(items, body, type_comment)
|
|
|
|
``async for`` loops and ``async with`` context managers. They have the same
|
|
fields as :class:`For` and :class:`With`, respectively. Only valid in the
|
|
body of an :class:`AsyncFunctionDef`.
|
|
|
|
.. note::
|
|
When a string is parsed by :func:`ast.parse`, operator nodes (subclasses
|
|
of :class:`ast.operator`, :class:`ast.unaryop`, :class:`ast.cmpop`,
|
|
:class:`ast.boolop` and :class:`ast.expr_context`) on the returned tree
|
|
will be singletons. Changes to one will be reflected in all other
|
|
occurrences of the same value (e.g. :class:`ast.Add`).
|
|
|
|
|
|
:mod:`ast` Helpers
|
|
------------------
|
|
|
|
Apart from the node classes, the :mod:`ast` module defines these utility functions
|
|
and classes for traversing abstract syntax trees:
|
|
|
|
.. function:: parse(source, filename='<unknown>', mode='exec', *, type_comments=False, feature_version=None)
|
|
|
|
Parse the source into an AST node. Equivalent to ``compile(source,
|
|
filename, mode, ast.PyCF_ONLY_AST)``.
|
|
|
|
If ``type_comments=True`` is given, the parser is modified to check
|
|
and return type comments as specified by :pep:`484` and :pep:`526`.
|
|
This is equivalent to adding :data:`ast.PyCF_TYPE_COMMENTS` to the
|
|
flags passed to :func:`compile()`. This will report syntax errors
|
|
for misplaced type comments. Without this flag, type comments will
|
|
be ignored, and the ``type_comment`` field on selected AST nodes
|
|
will always be ``None``. In addition, the locations of ``# type:
|
|
ignore`` comments will be returned as the ``type_ignores``
|
|
attribute of :class:`Module` (otherwise it is always an empty list).
|
|
|
|
In addition, if ``mode`` is ``'func_type'``, the input syntax is
|
|
modified to correspond to :pep:`484` "signature type comments",
|
|
e.g. ``(str, int) -> List[str]``.
|
|
|
|
Also, setting ``feature_version`` to a tuple ``(major, minor)``
|
|
will attempt to parse using that Python version's grammar.
|
|
Currently ``major`` must equal to ``3``. For example, setting
|
|
``feature_version=(3, 4)`` will allow the use of ``async`` and
|
|
``await`` as variable names. The lowest supported version is
|
|
``(3, 4)``; the highest is ``sys.version_info[0:2]``.
|
|
|
|
If source contains a null character ('\0'), :exc:`ValueError` is raised.
|
|
|
|
.. warning::
|
|
Note that successfully parsing source code into an AST object doesn't
|
|
guarantee that the source code provided is valid Python code that can
|
|
be executed as the compilation step can raise further :exc:`SyntaxError`
|
|
exceptions. For instance, the source ``return 42`` generates a valid
|
|
AST node for a return statement, but it cannot be compiled alone (it needs
|
|
to be inside a function node).
|
|
|
|
In particular, :func:`ast.parse` won't do any scoping checks, which the
|
|
compilation step does.
|
|
|
|
.. warning::
|
|
It is possible to crash the Python interpreter with a
|
|
sufficiently large/complex string due to stack depth limitations
|
|
in Python's AST compiler.
|
|
|
|
.. versionchanged:: 3.8
|
|
Added ``type_comments``, ``mode='func_type'`` and ``feature_version``.
|
|
|
|
|
|
.. function:: unparse(ast_obj)
|
|
|
|
Unparse an :class:`ast.AST` object and generate a string with code
|
|
that would produce an equivalent :class:`ast.AST` object if parsed
|
|
back with :func:`ast.parse`.
|
|
|
|
.. warning::
|
|
The produced code string will not necessarily be equal to the original
|
|
code that generated the :class:`ast.AST` object (without any compiler
|
|
optimizations, such as constant tuples/frozensets).
|
|
|
|
.. warning::
|
|
Trying to unparse a highly complex expression would result with
|
|
:exc:`RecursionError`.
|
|
|
|
.. versionadded:: 3.9
|
|
|
|
|
|
.. function:: literal_eval(node_or_string)
|
|
|
|
Safely evaluate an expression node or a string containing a Python literal or
|
|
container display. The string or node provided may only consist of the
|
|
following Python literal structures: strings, bytes, numbers, tuples, lists,
|
|
dicts, sets, booleans, ``None`` and ``Ellipsis``.
|
|
|
|
This can be used for safely evaluating strings containing Python values from
|
|
untrusted sources without the need to parse the values oneself. It is not
|
|
capable of evaluating arbitrarily complex expressions, for example involving
|
|
operators or indexing.
|
|
|
|
.. warning::
|
|
It is possible to crash the Python interpreter with a
|
|
sufficiently large/complex string due to stack depth limitations
|
|
in Python's AST compiler.
|
|
|
|
It can raise :exc:`ValueError`, :exc:`TypeError`, :exc:`SyntaxError`,
|
|
:exc:`MemoryError` and :exc:`RecursionError` depending on the malformed
|
|
input.
|
|
|
|
.. versionchanged:: 3.2
|
|
Now allows bytes and set literals.
|
|
|
|
.. versionchanged:: 3.9
|
|
Now supports creating empty sets with ``'set()'``.
|
|
|
|
.. versionchanged:: 3.10
|
|
For string inputs, leading spaces and tabs are now stripped.
|
|
|
|
|
|
.. function:: get_docstring(node, clean=True)
|
|
|
|
Return the docstring of the given *node* (which must be a
|
|
:class:`FunctionDef`, :class:`AsyncFunctionDef`, :class:`ClassDef`,
|
|
or :class:`Module` node), or ``None`` if it has no docstring.
|
|
If *clean* is true, clean up the docstring's indentation with
|
|
:func:`inspect.cleandoc`.
|
|
|
|
.. versionchanged:: 3.5
|
|
:class:`AsyncFunctionDef` is now supported.
|
|
|
|
|
|
.. function:: get_source_segment(source, node, *, padded=False)
|
|
|
|
Get source code segment of the *source* that generated *node*.
|
|
If some location information (:attr:`lineno`, :attr:`end_lineno`,
|
|
:attr:`col_offset`, or :attr:`end_col_offset`) is missing, return ``None``.
|
|
|
|
If *padded* is ``True``, the first line of a multi-line statement will
|
|
be padded with spaces to match its original position.
|
|
|
|
.. versionadded:: 3.8
|
|
|
|
|
|
.. function:: fix_missing_locations(node)
|
|
|
|
When you compile a node tree with :func:`compile`, the compiler expects
|
|
:attr:`lineno` and :attr:`col_offset` attributes for every node that supports
|
|
them. This is rather tedious to fill in for generated nodes, so this helper
|
|
adds these attributes recursively where not already set, by setting them to
|
|
the values of the parent node. It works recursively starting at *node*.
|
|
|
|
|
|
.. function:: increment_lineno(node, n=1)
|
|
|
|
Increment the line number and end line number of each node in the tree
|
|
starting at *node* by *n*. This is useful to "move code" to a different
|
|
location in a file.
|
|
|
|
|
|
.. function:: copy_location(new_node, old_node)
|
|
|
|
Copy source location (:attr:`lineno`, :attr:`col_offset`, :attr:`end_lineno`,
|
|
and :attr:`end_col_offset`) from *old_node* to *new_node* if possible,
|
|
and return *new_node*.
|
|
|
|
|
|
.. function:: iter_fields(node)
|
|
|
|
Yield a tuple of ``(fieldname, value)`` for each field in ``node._fields``
|
|
that is present on *node*.
|
|
|
|
|
|
.. function:: iter_child_nodes(node)
|
|
|
|
Yield all direct child nodes of *node*, that is, all fields that are nodes
|
|
and all items of fields that are lists of nodes.
|
|
|
|
|
|
.. function:: walk(node)
|
|
|
|
Recursively yield all descendant nodes in the tree starting at *node*
|
|
(including *node* itself), in no specified order. This is useful if you only
|
|
want to modify nodes in place and don't care about the context.
|
|
|
|
|
|
.. class:: NodeVisitor()
|
|
|
|
A node visitor base class that walks the abstract syntax tree and calls a
|
|
visitor function for every node found. This function may return a value
|
|
which is forwarded by the :meth:`visit` method.
|
|
|
|
This class is meant to be subclassed, with the subclass adding visitor
|
|
methods.
|
|
|
|
.. method:: visit(node)
|
|
|
|
Visit a node. The default implementation calls the method called
|
|
:samp:`self.visit_{classname}` where *classname* is the name of the node
|
|
class, or :meth:`generic_visit` if that method doesn't exist.
|
|
|
|
.. method:: generic_visit(node)
|
|
|
|
This visitor calls :meth:`visit` on all children of the node.
|
|
|
|
Note that child nodes of nodes that have a custom visitor method won't be
|
|
visited unless the visitor calls :meth:`generic_visit` or visits them
|
|
itself.
|
|
|
|
Don't use the :class:`NodeVisitor` if you want to apply changes to nodes
|
|
during traversal. For this a special visitor exists
|
|
(:class:`NodeTransformer`) that allows modifications.
|
|
|
|
.. deprecated:: 3.8
|
|
|
|
Methods :meth:`visit_Num`, :meth:`visit_Str`, :meth:`visit_Bytes`,
|
|
:meth:`visit_NameConstant` and :meth:`visit_Ellipsis` are deprecated
|
|
now and will not be called in future Python versions. Add the
|
|
:meth:`visit_Constant` method to handle all constant nodes.
|
|
|
|
|
|
.. class:: NodeTransformer()
|
|
|
|
A :class:`NodeVisitor` subclass that walks the abstract syntax tree and
|
|
allows modification of nodes.
|
|
|
|
The :class:`NodeTransformer` will walk the AST and use the return value of
|
|
the visitor methods to replace or remove the old node. If the return value
|
|
of the visitor method is ``None``, the node will be removed from its
|
|
location, otherwise it is replaced with the return value. The return value
|
|
may be the original node in which case no replacement takes place.
|
|
|
|
Here is an example transformer that rewrites all occurrences of name lookups
|
|
(``foo``) to ``data['foo']``::
|
|
|
|
class RewriteName(NodeTransformer):
|
|
|
|
def visit_Name(self, node):
|
|
return Subscript(
|
|
value=Name(id='data', ctx=Load()),
|
|
slice=Constant(value=node.id),
|
|
ctx=node.ctx
|
|
)
|
|
|
|
Keep in mind that if the node you're operating on has child nodes you must
|
|
either transform the child nodes yourself or call the :meth:`generic_visit`
|
|
method for the node first.
|
|
|
|
For nodes that were part of a collection of statements (that applies to all
|
|
statement nodes), the visitor may also return a list of nodes rather than
|
|
just a single node.
|
|
|
|
If :class:`NodeTransformer` introduces new nodes (that weren't part of
|
|
original tree) without giving them location information (such as
|
|
:attr:`lineno`), :func:`fix_missing_locations` should be called with
|
|
the new sub-tree to recalculate the location information::
|
|
|
|
tree = ast.parse('foo', mode='eval')
|
|
new_tree = fix_missing_locations(RewriteName().visit(tree))
|
|
|
|
Usually you use the transformer like this::
|
|
|
|
node = YourTransformer().visit(node)
|
|
|
|
|
|
.. function:: dump(node, annotate_fields=True, include_attributes=False, *, indent=None)
|
|
|
|
Return a formatted dump of the tree in *node*. This is mainly useful for
|
|
debugging purposes. If *annotate_fields* is true (by default),
|
|
the returned string will show the names and the values for fields.
|
|
If *annotate_fields* is false, the result string will be more compact by
|
|
omitting unambiguous field names. Attributes such as line
|
|
numbers and column offsets are not dumped by default. If this is wanted,
|
|
*include_attributes* can be set to true.
|
|
|
|
If *indent* is a non-negative integer or string, then the tree will be
|
|
pretty-printed with that indent level. An indent level
|
|
of 0, negative, or ``""`` will only insert newlines. ``None`` (the default)
|
|
selects the single line representation. Using a positive integer indent
|
|
indents that many spaces per level. If *indent* is a string (such as ``"\t"``),
|
|
that string is used to indent each level.
|
|
|
|
.. versionchanged:: 3.9
|
|
Added the *indent* option.
|
|
|
|
|
|
.. _ast-compiler-flags:
|
|
|
|
Compiler Flags
|
|
--------------
|
|
|
|
The following flags may be passed to :func:`compile` in order to change
|
|
effects on the compilation of a program:
|
|
|
|
.. data:: PyCF_ALLOW_TOP_LEVEL_AWAIT
|
|
|
|
Enables support for top-level ``await``, ``async for``, ``async with``
|
|
and async comprehensions.
|
|
|
|
.. versionadded:: 3.8
|
|
|
|
.. data:: PyCF_ONLY_AST
|
|
|
|
Generates and returns an abstract syntax tree instead of returning a
|
|
compiled code object.
|
|
|
|
.. data:: PyCF_TYPE_COMMENTS
|
|
|
|
Enables support for :pep:`484` and :pep:`526` style type comments
|
|
(``# type: <type>``, ``# type: ignore <stuff>``).
|
|
|
|
.. versionadded:: 3.8
|
|
|
|
|
|
.. _ast-cli:
|
|
|
|
Command-Line Usage
|
|
------------------
|
|
|
|
.. versionadded:: 3.9
|
|
|
|
The :mod:`ast` module can be executed as a script from the command line.
|
|
It is as simple as:
|
|
|
|
.. code-block:: sh
|
|
|
|
python -m ast [-m <mode>] [-a] [infile]
|
|
|
|
The following options are accepted:
|
|
|
|
.. program:: ast
|
|
|
|
.. cmdoption:: -h, --help
|
|
|
|
Show the help message and exit.
|
|
|
|
.. cmdoption:: -m <mode>
|
|
--mode <mode>
|
|
|
|
Specify what kind of code must be compiled, like the *mode* argument
|
|
in :func:`parse`.
|
|
|
|
.. cmdoption:: --no-type-comments
|
|
|
|
Don't parse type comments.
|
|
|
|
.. cmdoption:: -a, --include-attributes
|
|
|
|
Include attributes such as line numbers and column offsets.
|
|
|
|
.. cmdoption:: -i <indent>
|
|
--indent <indent>
|
|
|
|
Indentation of nodes in AST (number of spaces).
|
|
|
|
If :file:`infile` is specified its contents are parsed to AST and dumped
|
|
to stdout. Otherwise, the content is read from stdin.
|
|
|
|
|
|
.. seealso::
|
|
|
|
`Green Tree Snakes <https://greentreesnakes.readthedocs.io/>`_, an external
|
|
documentation resource, has good details on working with Python ASTs.
|
|
|
|
`ASTTokens <https://asttokens.readthedocs.io/en/latest/user-guide.html>`_
|
|
annotates Python ASTs with the positions of tokens and text in the source
|
|
code that generated them. This is helpful for tools that make source code
|
|
transformations.
|
|
|
|
`leoAst.py <http://leoeditor.com/appendices.html#leoast-py>`_ unifies the
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token-based and parse-tree-based views of python programs by inserting
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two-way links between tokens and ast nodes.
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`LibCST <https://libcst.readthedocs.io/>`_ parses code as a Concrete Syntax
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Tree that looks like an ast tree and keeps all formatting details. It's
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useful for building automated refactoring (codemod) applications and
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linters.
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`Parso <https://parso.readthedocs.io>`_ is a Python parser that supports
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error recovery and round-trip parsing for different Python versions (in
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multiple Python versions). Parso is also able to list multiple syntax errors
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in your python file.
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