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Document the "st" API, to avoid confusion with the "new" AST. 

Add a note about using the new AST module.
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Georg Brandl 2008-06-07 18:17:37 +00:00
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@ -24,6 +24,17 @@ from this. This is better than trying to parse and modify an arbitrary Python
code fragment as a string because parsing is performed in a manner identical to code fragment as a string because parsing is performed in a manner identical to
the code forming the application. It is also faster. the code forming the application. It is also faster.
.. note::
From Python 2.5 onward, it's much more convenient to cut in at the Abstract
Syntax Tree (AST) generation and compilation stage, using the :mod:`ast`
module.
The :mod:`parser` module exports the names documented here also with "st"
replaced by "ast"; this is a legacy from the time when there was no other
AST and has nothing to do with the AST found in Python 2.5. This is also the
reason for the functions' keyword arguments being called *ast*, not *st*.
There are a few things to note about this module which are important to making There are a few things to note about this module which are important to making
use of the data structures created. This is not a tutorial on editing the parse use of the data structures created. This is not a tutorial on editing the parse
trees for Python code, but some examples of using the :mod:`parser` module are trees for Python code, but some examples of using the :mod:`parser` module are
@ -34,9 +45,9 @@ internal parser is required. For full information on the language syntax, refer
to :ref:`reference-index`. The parser to :ref:`reference-index`. The parser
itself is created from a grammar specification defined in the file itself is created from a grammar specification defined in the file
:file:`Grammar/Grammar` in the standard Python distribution. The parse trees :file:`Grammar/Grammar` in the standard Python distribution. The parse trees
stored in the AST objects created by this module are the actual output from the stored in the ST objects created by this module are the actual output from the
internal parser when created by the :func:`expr` or :func:`suite` functions, internal parser when created by the :func:`expr` or :func:`suite` functions,
described below. The AST objects created by :func:`sequence2ast` faithfully described below. The ST objects created by :func:`sequence2st` faithfully
simulate those structures. Be aware that the values of the sequences which are simulate those structures. Be aware that the values of the sequences which are
considered "correct" will vary from one version of Python to another as the considered "correct" will vary from one version of Python to another as the
formal grammar for the language is revised. However, transporting code from one formal grammar for the language is revised. However, transporting code from one
@ -46,7 +57,7 @@ migrating to an older version of the interpreter will not support more recent
language constructs. The parse trees are not typically compatible from one language constructs. The parse trees are not typically compatible from one
version to another, whereas source code has always been forward-compatible. version to another, whereas source code has always been forward-compatible.
Each element of the sequences returned by :func:`ast2list` or :func:`ast2tuple` Each element of the sequences returned by :func:`st2list` or :func:`st2tuple`
has a simple form. Sequences representing non-terminal elements in the grammar has a simple form. Sequences representing non-terminal elements in the grammar
always have a length greater than one. The first element is an integer which always have a length greater than one. The first element is an integer which
identifies a production in the grammar. These integers are given symbolic names identifies a production in the grammar. These integers are given symbolic names
@ -69,19 +80,19 @@ of the :keyword:`if` keyword above is representative. The various types of
terminal symbols are defined in the C header file :file:`Include/token.h` and terminal symbols are defined in the C header file :file:`Include/token.h` and
the Python module :mod:`token`. the Python module :mod:`token`.
The AST objects are not required to support the functionality of this module, The ST objects are not required to support the functionality of this module,
but are provided for three purposes: to allow an application to amortize the but are provided for three purposes: to allow an application to amortize the
cost of processing complex parse trees, to provide a parse tree representation cost of processing complex parse trees, to provide a parse tree representation
which conserves memory space when compared to the Python list or tuple which conserves memory space when compared to the Python list or tuple
representation, and to ease the creation of additional modules in C which representation, and to ease the creation of additional modules in C which
manipulate parse trees. A simple "wrapper" class may be created in Python to manipulate parse trees. A simple "wrapper" class may be created in Python to
hide the use of AST objects. hide the use of ST objects.
The :mod:`parser` module defines functions for a few distinct purposes. The The :mod:`parser` module defines functions for a few distinct purposes. The
most important purposes are to create AST objects and to convert AST objects to most important purposes are to create ST objects and to convert ST objects to
other representations such as parse trees and compiled code objects, but there other representations such as parse trees and compiled code objects, but there
are also functions which serve to query the type of parse tree represented by an are also functions which serve to query the type of parse tree represented by an
AST object. ST object.
.. seealso:: .. seealso::
@ -94,20 +105,20 @@ AST object.
testing node values. testing node values.
.. _creating-asts: .. _creating-sts:
Creating AST Objects Creating ST Objects
-------------------- -------------------
AST objects may be created from source code or from a parse tree. When creating ST objects may be created from source code or from a parse tree. When creating
an AST object from source, different functions are used to create the ``'eval'`` an ST object from source, different functions are used to create the ``'eval'``
and ``'exec'`` forms. and ``'exec'`` forms.
.. function:: expr(source) .. function:: expr(source)
The :func:`expr` function parses the parameter *source* as if it were an input The :func:`expr` function parses the parameter *source* as if it were an input
to ``compile(source, 'file.py', 'eval')``. If the parse succeeds, an AST object to ``compile(source, 'file.py', 'eval')``. If the parse succeeds, an ST object
is created to hold the internal parse tree representation, otherwise an is created to hold the internal parse tree representation, otherwise an
appropriate exception is thrown. appropriate exception is thrown.
@ -115,22 +126,22 @@ and ``'exec'`` forms.
.. function:: suite(source) .. function:: suite(source)
The :func:`suite` function parses the parameter *source* as if it were an input The :func:`suite` function parses the parameter *source* as if it were an input
to ``compile(source, 'file.py', 'exec')``. If the parse succeeds, an AST object to ``compile(source, 'file.py', 'exec')``. If the parse succeeds, an ST object
is created to hold the internal parse tree representation, otherwise an is created to hold the internal parse tree representation, otherwise an
appropriate exception is thrown. appropriate exception is thrown.
.. function:: sequence2ast(sequence) .. function:: sequence2st(sequence)
This function accepts a parse tree represented as a sequence and builds an This function accepts a parse tree represented as a sequence and builds an
internal representation if possible. If it can validate that the tree conforms internal representation if possible. If it can validate that the tree conforms
to the Python grammar and all nodes are valid node types in the host version of to the Python grammar and all nodes are valid node types in the host version of
Python, an AST object is created from the internal representation and returned Python, an ST object is created from the internal representation and returned
to the called. If there is a problem creating the internal representation, or to the called. If there is a problem creating the internal representation, or
if the tree cannot be validated, a :exc:`ParserError` exception is thrown. An if the tree cannot be validated, a :exc:`ParserError` exception is thrown. An
AST object created this way should not be assumed to compile correctly; normal ST object created this way should not be assumed to compile correctly; normal
exceptions thrown by compilation may still be initiated when the AST object is exceptions thrown by compilation may still be initiated when the ST object is
passed to :func:`compileast`. This may indicate problems not related to syntax passed to :func:`compilest`. This may indicate problems not related to syntax
(such as a :exc:`MemoryError` exception), but may also be due to constructs such (such as a :exc:`MemoryError` exception), but may also be due to constructs such
as the result of parsing ``del f(0)``, which escapes the Python parser but is as the result of parsing ``del f(0)``, which escapes the Python parser but is
checked by the bytecode compiler. checked by the bytecode compiler.
@ -142,31 +153,31 @@ and ``'exec'`` forms.
symbols in the input tree. symbols in the input tree.
.. function:: tuple2ast(sequence) .. function:: tuple2st(sequence)
This is the same function as :func:`sequence2ast`. This entry point is This is the same function as :func:`sequence2st`. This entry point is
maintained for backward compatibility. maintained for backward compatibility.
.. _converting-asts: .. _converting-sts:
Converting AST Objects Converting ST Objects
---------------------- ---------------------
AST objects, regardless of the input used to create them, may be converted to ST objects, regardless of the input used to create them, may be converted to
parse trees represented as list- or tuple- trees, or may be compiled into parse trees represented as list- or tuple- trees, or may be compiled into
executable code objects. Parse trees may be extracted with or without line executable code objects. Parse trees may be extracted with or without line
numbering information. numbering information.
.. function:: ast2list(ast[, line_info]) .. function:: st2list(ast[, line_info])
This function accepts an AST object from the caller in *ast* and returns a This function accepts an ST object from the caller in *ast* and returns a
Python list representing the equivalent parse tree. The resulting list Python list representing the equivalent parse tree. The resulting list
representation can be used for inspection or the creation of a new parse tree in representation can be used for inspection or the creation of a new parse tree in
list form. This function does not fail so long as memory is available to build list form. This function does not fail so long as memory is available to build
the list representation. If the parse tree will only be used for inspection, the list representation. If the parse tree will only be used for inspection,
:func:`ast2tuple` should be used instead to reduce memory consumption and :func:`st2tuple` should be used instead to reduce memory consumption and
fragmentation. When the list representation is required, this function is fragmentation. When the list representation is required, this function is
significantly faster than retrieving a tuple representation and converting that significantly faster than retrieving a tuple representation and converting that
to nested lists. to nested lists.
@ -177,29 +188,29 @@ numbering information.
This information is omitted if the flag is false or omitted. This information is omitted if the flag is false or omitted.
.. function:: ast2tuple(ast[, line_info]) .. function:: st2tuple(ast[, line_info])
This function accepts an AST object from the caller in *ast* and returns a This function accepts an ST object from the caller in *ast* and returns a
Python tuple representing the equivalent parse tree. Other than returning a Python tuple representing the equivalent parse tree. Other than returning a
tuple instead of a list, this function is identical to :func:`ast2list`. tuple instead of a list, this function is identical to :func:`st2list`.
If *line_info* is true, line number information will be included for all If *line_info* is true, line number information will be included for all
terminal tokens as a third element of the list representing the token. This terminal tokens as a third element of the list representing the token. This
information is omitted if the flag is false or omitted. information is omitted if the flag is false or omitted.
.. function:: compileast(ast[, filename='<ast>']) .. function:: compilest(ast[, filename='<syntax-tree>'])
.. index:: builtin: eval .. index:: builtin: eval
The Python byte compiler can be invoked on an AST object to produce code objects The Python byte compiler can be invoked on an ST object to produce code objects
which can be used as part of an :keyword:`exec` statement or a call to the which can be used as part of an :keyword:`exec` statement or a call to the
built-in :func:`eval` function. This function provides the interface to the built-in :func:`eval` function. This function provides the interface to the
compiler, passing the internal parse tree from *ast* to the parser, using the compiler, passing the internal parse tree from *ast* to the parser, using the
source file name specified by the *filename* parameter. The default value source file name specified by the *filename* parameter. The default value
supplied for *filename* indicates that the source was an AST object. supplied for *filename* indicates that the source was an ST object.
Compiling an AST object may result in exceptions related to compilation; an Compiling an ST object may result in exceptions related to compilation; an
example would be a :exc:`SyntaxError` caused by the parse tree for ``del f(0)``: example would be a :exc:`SyntaxError` caused by the parse tree for ``del f(0)``:
this statement is considered legal within the formal grammar for Python but is this statement is considered legal within the formal grammar for Python but is
not a legal language construct. The :exc:`SyntaxError` raised for this not a legal language construct. The :exc:`SyntaxError` raised for this
@ -209,15 +220,15 @@ numbering information.
tree. tree.
.. _querying-asts: .. _querying-sts:
Queries on AST Objects Queries on ST Objects
---------------------- ---------------------
Two functions are provided which allow an application to determine if an AST was Two functions are provided which allow an application to determine if an ST was
created as an expression or a suite. Neither of these functions can be used to created as an expression or a suite. Neither of these functions can be used to
determine if an AST was created from source code via :func:`expr` or determine if an ST was created from source code via :func:`expr` or
:func:`suite` or from a parse tree via :func:`sequence2ast`. :func:`suite` or from a parse tree via :func:`sequence2st`.
.. function:: isexpr(ast) .. function:: isexpr(ast)
@ -227,19 +238,19 @@ determine if an AST was created from source code via :func:`expr` or
When *ast* represents an ``'eval'`` form, this function returns true, otherwise When *ast* represents an ``'eval'`` form, this function returns true, otherwise
it returns false. This is useful, since code objects normally cannot be queried it returns false. This is useful, since code objects normally cannot be queried
for this information using existing built-in functions. Note that the code for this information using existing built-in functions. Note that the code
objects created by :func:`compileast` cannot be queried like this either, and objects created by :func:`compilest` cannot be queried like this either, and
are identical to those created by the built-in :func:`compile` function. are identical to those created by the built-in :func:`compile` function.
.. function:: issuite(ast) .. function:: issuite(ast)
This function mirrors :func:`isexpr` in that it reports whether an AST object This function mirrors :func:`isexpr` in that it reports whether an ST object
represents an ``'exec'`` form, commonly known as a "suite." It is not safe to represents an ``'exec'`` form, commonly known as a "suite." It is not safe to
assume that this function is equivalent to ``not isexpr(ast)``, as additional assume that this function is equivalent to ``not isexpr(ast)``, as additional
syntactic fragments may be supported in the future. syntactic fragments may be supported in the future.
.. _ast-errors: .. _st-errors:
Exceptions and Error Handling Exceptions and Error Handling
----------------------------- -----------------------------
@ -255,12 +266,12 @@ function for information about the exceptions it can raise.
generally produced for validation failures rather than the built in generally produced for validation failures rather than the built in
:exc:`SyntaxError` thrown during normal parsing. The exception argument is :exc:`SyntaxError` thrown during normal parsing. The exception argument is
either a string describing the reason of the failure or a tuple containing a either a string describing the reason of the failure or a tuple containing a
sequence causing the failure from a parse tree passed to :func:`sequence2ast` sequence causing the failure from a parse tree passed to :func:`sequence2st`
and an explanatory string. Calls to :func:`sequence2ast` need to be able to and an explanatory string. Calls to :func:`sequence2st` need to be able to
handle either type of exception, while calls to other functions in the module handle either type of exception, while calls to other functions in the module
will only need to be aware of the simple string values. will only need to be aware of the simple string values.
Note that the functions :func:`compileast`, :func:`expr`, and :func:`suite` may Note that the functions :func:`compilest`, :func:`expr`, and :func:`suite` may
throw exceptions which are normally thrown by the parsing and compilation throw exceptions which are normally thrown by the parsing and compilation
process. These include the built in exceptions :exc:`MemoryError`, process. These include the built in exceptions :exc:`MemoryError`,
:exc:`OverflowError`, :exc:`SyntaxError`, and :exc:`SystemError`. In these :exc:`OverflowError`, :exc:`SyntaxError`, and :exc:`SystemError`. In these
@ -268,49 +279,49 @@ cases, these exceptions carry all the meaning normally associated with them.
Refer to the descriptions of each function for detailed information. Refer to the descriptions of each function for detailed information.
.. _ast-objects: .. _st-objects:
AST Objects ST Objects
----------- ----------
Ordered and equality comparisons are supported between AST objects. Pickling of Ordered and equality comparisons are supported between ST objects. Pickling of
AST objects (using the :mod:`pickle` module) is also supported. ST objects (using the :mod:`pickle` module) is also supported.
.. data:: ASTType .. data:: STType
The type of the objects returned by :func:`expr`, :func:`suite` and The type of the objects returned by :func:`expr`, :func:`suite` and
:func:`sequence2ast`. :func:`sequence2st`.
AST objects have the following methods: ST objects have the following methods:
.. method:: AST.compile([filename]) .. method:: ST.compile([filename])
Same as ``compileast(ast, filename)``. Same as ``compilest(st, filename)``.
.. method:: AST.isexpr() .. method:: ST.isexpr()
Same as ``isexpr(ast)``. Same as ``isexpr(st)``.
.. method:: AST.issuite() .. method:: ST.issuite()
Same as ``issuite(ast)``. Same as ``issuite(st)``.
.. method:: AST.tolist([line_info]) .. method:: ST.tolist([line_info])
Same as ``ast2list(ast, line_info)``. Same as ``st2list(st, line_info)``.
.. method:: AST.totuple([line_info]) .. method:: ST.totuple([line_info])
Same as ``ast2tuple(ast, line_info)``. Same as ``st2tuple(st, line_info)``.
.. _ast-examples: .. _st-examples:
Examples Examples
-------- --------
@ -338,27 +349,27 @@ to the code ::
10 10
The equivalent operation using the :mod:`parser` module is somewhat longer, and The equivalent operation using the :mod:`parser` module is somewhat longer, and
allows the intermediate internal parse tree to be retained as an AST object:: allows the intermediate internal parse tree to be retained as an ST object::
>>> import parser >>> import parser
>>> ast = parser.expr('a + 5') >>> st = parser.expr('a + 5')
>>> code = ast.compile('file.py') >>> code = st.compile('file.py')
>>> a = 5 >>> a = 5
>>> eval(code) >>> eval(code)
10 10
An application which needs both AST and code objects can package this code into An application which needs both ST and code objects can package this code into
readily available functions:: readily available functions::
import parser import parser
def load_suite(source_string): def load_suite(source_string):
ast = parser.suite(source_string) st = parser.suite(source_string)
return ast, ast.compile() return st, st.compile()
def load_expression(source_string): def load_expression(source_string):
ast = parser.expr(source_string) st = parser.expr(source_string)
return ast, ast.compile() return st, st.compile()
Information Discovery Information Discovery
@ -412,8 +423,8 @@ tuples. ::
>>> import parser >>> import parser
>>> import pprint >>> import pprint
>>> ast = parser.suite(open('docstring.py').read()) >>> st = parser.suite(open('docstring.py').read())
>>> tup = ast.totuple() >>> tup = st.totuple()
>>> pprint.pprint(tup) >>> pprint.pprint(tup)
(257, (257,
(264, (264,
@ -670,8 +681,8 @@ file :file:`example.py`.) ::
source = open(fileName).read() source = open(fileName).read()
basename = os.path.basename(os.path.splitext(fileName)[0]) basename = os.path.basename(os.path.splitext(fileName)[0])
ast = parser.suite(source) st = parser.suite(source)
return ModuleInfo(ast.totuple(), basename) return ModuleInfo(st.totuple(), basename)
This provides an easy-to-use interface to the documentation of a module. If This provides an easy-to-use interface to the documentation of a module. If
information is required which is not extracted by the code of this example, the information is required which is not extracted by the code of this example, the