844 lines
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ReStructuredText
844 lines
40 KiB
ReStructuredText
.. _glossary:
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********
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Glossary
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********
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.. if you add new entries, keep the alphabetical sorting!
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.. glossary::
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``>>>``
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The default Python prompt of the interactive shell. Often seen for code
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examples which can be executed interactively in the interpreter.
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``...``
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The default Python prompt of the interactive shell when entering code for
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an indented code block or within a pair of matching left and right
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delimiters (parentheses, square brackets or curly braces).
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2to3
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A tool that tries to convert Python 2.x code to Python 3.x code by
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handling most of the incompatibilities which can be detected by parsing the
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source and traversing the parse tree.
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2to3 is available in the standard library as :mod:`lib2to3`; a standalone
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entry point is provided as :file:`Tools/scripts/2to3`. See
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:ref:`2to3-reference`.
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abstract base class
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Abstract base classes complement :term:`duck-typing` by
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providing a way to define interfaces when other techniques like
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:func:`hasattr` would be clumsy or subtly wrong (for example with
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:ref:`magic methods <special-lookup>`). ABCs introduce virtual
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subclasses, which are classes that don't inherit from a class but are
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still recognized by :func:`isinstance` and :func:`issubclass`; see the
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:mod:`abc` module documentation. Python comes with many built-in ABCs for
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data structures (in the :mod:`collections.abc` module), numbers (in the
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:mod:`numbers` module), streams (in the :mod:`io` module), import finders
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and loaders (in the :mod:`importlib.abc` module). You can create your own
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ABCs with the :mod:`abc` module.
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argument
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A value passed to a :term:`function` (or :term:`method`) when calling the
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function. There are two kinds of argument:
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* :dfn:`keyword argument`: an argument preceded by an identifier (e.g.
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``name=``) in a function call or passed as a value in a dictionary
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preceded by ``**``. For example, ``3`` and ``5`` are both keyword
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arguments in the following calls to :func:`complex`::
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complex(real=3, imag=5)
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complex(**{'real': 3, 'imag': 5})
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* :dfn:`positional argument`: an argument that is not a keyword argument.
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Positional arguments can appear at the beginning of an argument list
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and/or be passed as elements of an :term:`iterable` preceded by ``*``.
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For example, ``3`` and ``5`` are both positional arguments in the
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following calls::
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complex(3, 5)
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complex(*(3, 5))
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Arguments are assigned to the named local variables in a function body.
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See the :ref:`calls` section for the rules governing this assignment.
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Syntactically, any expression can be used to represent an argument; the
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evaluated value is assigned to the local variable.
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See also the :term:`parameter` glossary entry, the FAQ question on
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:ref:`the difference between arguments and parameters
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<faq-argument-vs-parameter>`, and :pep:`362`.
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attribute
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A value associated with an object which is referenced by name using
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dotted expressions. For example, if an object *o* has an attribute
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*a* it would be referenced as *o.a*.
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BDFL
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Benevolent Dictator For Life, a.k.a. `Guido van Rossum
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<http://www.python.org/~guido/>`_, Python's creator.
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binary file
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A :term:`file object` able to read and write
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:term:`bytes-like objects <bytes-like object>`.
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.. seealso::
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A :term:`text file` reads and writes :class:`str` objects.
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bytes-like object
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An object that supports the :ref:`bufferobjects`, like :class:`bytes`,
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:class:`bytearray` or :class:`memoryview`. Bytes-like objects can
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be used for various operations that expect binary data, such as
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compression, saving to a binary file or sending over a socket.
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Some operations need the binary data to be mutable, in which case
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not all bytes-like objects can apply.
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bytecode
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Python source code is compiled into bytecode, the internal representation
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of a Python program in the CPython interpreter. The bytecode is also
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cached in ``.pyc`` and ``.pyo`` files so that executing the same file is
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faster the second time (recompilation from source to bytecode can be
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avoided). This "intermediate language" is said to run on a
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:term:`virtual machine` that executes the machine code corresponding to
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each bytecode. Do note that bytecodes are not expected to work between
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different Python virtual machines, nor to be stable between Python
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releases.
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A list of bytecode instructions can be found in the documentation for
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:ref:`the dis module <bytecodes>`.
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class
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A template for creating user-defined objects. Class definitions
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normally contain method definitions which operate on instances of the
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class.
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coercion
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The implicit conversion of an instance of one type to another during an
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operation which involves two arguments of the same type. For example,
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``int(3.15)`` converts the floating point number to the integer ``3``, but
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in ``3+4.5``, each argument is of a different type (one int, one float),
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and both must be converted to the same type before they can be added or it
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will raise a ``TypeError``. Without coercion, all arguments of even
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compatible types would have to be normalized to the same value by the
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programmer, e.g., ``float(3)+4.5`` rather than just ``3+4.5``.
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complex number
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An extension of the familiar real number system in which all numbers are
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expressed as a sum of a real part and an imaginary part. Imaginary
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numbers are real multiples of the imaginary unit (the square root of
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``-1``), often written ``i`` in mathematics or ``j`` in
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engineering. Python has built-in support for complex numbers, which are
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written with this latter notation; the imaginary part is written with a
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``j`` suffix, e.g., ``3+1j``. To get access to complex equivalents of the
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:mod:`math` module, use :mod:`cmath`. Use of complex numbers is a fairly
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advanced mathematical feature. If you're not aware of a need for them,
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it's almost certain you can safely ignore them.
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context manager
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An object which controls the environment seen in a :keyword:`with`
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statement by defining :meth:`__enter__` and :meth:`__exit__` methods.
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See :pep:`343`.
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CPython
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The canonical implementation of the Python programming language, as
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distributed on `python.org <http://python.org>`_. The term "CPython"
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is used when necessary to distinguish this implementation from others
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such as Jython or IronPython.
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decorator
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A function returning another function, usually applied as a function
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transformation using the ``@wrapper`` syntax. Common examples for
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decorators are :func:`classmethod` and :func:`staticmethod`.
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The decorator syntax is merely syntactic sugar, the following two
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function definitions are semantically equivalent::
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def f(...):
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...
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f = staticmethod(f)
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@staticmethod
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def f(...):
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...
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The same concept exists for classes, but is less commonly used there. See
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the documentation for :ref:`function definitions <function>` and
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:ref:`class definitions <class>` for more about decorators.
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descriptor
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Any object which defines the methods :meth:`__get__`, :meth:`__set__`, or
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:meth:`__delete__`. When a class attribute is a descriptor, its special
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binding behavior is triggered upon attribute lookup. Normally, using
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*a.b* to get, set or delete an attribute looks up the object named *b* in
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the class dictionary for *a*, but if *b* is a descriptor, the respective
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descriptor method gets called. Understanding descriptors is a key to a
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deep understanding of Python because they are the basis for many features
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including functions, methods, properties, class methods, static methods,
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and reference to super classes.
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For more information about descriptors' methods, see :ref:`descriptors`.
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dictionary
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An associative array, where arbitrary keys are mapped to values. The
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keys can be any object with :meth:`__hash__` and :meth:`__eq__` methods.
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Called a hash in Perl.
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docstring
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A string literal which appears as the first expression in a class,
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function or module. While ignored when the suite is executed, it is
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recognized by the compiler and put into the :attr:`__doc__` attribute
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of the enclosing class, function or module. Since it is available via
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introspection, it is the canonical place for documentation of the
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object.
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duck-typing
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A programming style which does not look at an object's type to determine
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if it has the right interface; instead, the method or attribute is simply
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called or used ("If it looks like a duck and quacks like a duck, it
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must be a duck.") By emphasizing interfaces rather than specific types,
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well-designed code improves its flexibility by allowing polymorphic
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substitution. Duck-typing avoids tests using :func:`type` or
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:func:`isinstance`. (Note, however, that duck-typing can be complemented
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with :term:`abstract base classes <abstract base class>`.) Instead, it
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typically employs :func:`hasattr` tests or :term:`EAFP` programming.
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EAFP
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Easier to ask for forgiveness than permission. This common Python coding
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style assumes the existence of valid keys or attributes and catches
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exceptions if the assumption proves false. This clean and fast style is
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characterized by the presence of many :keyword:`try` and :keyword:`except`
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statements. The technique contrasts with the :term:`LBYL` style
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common to many other languages such as C.
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expression
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A piece of syntax which can be evaluated to some value. In other words,
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an expression is an accumulation of expression elements like literals,
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names, attribute access, operators or function calls which all return a
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value. In contrast to many other languages, not all language constructs
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are expressions. There are also :term:`statement`\s which cannot be used
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as expressions, such as :keyword:`if`. Assignments are also statements,
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not expressions.
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extension module
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A module written in C or C++, using Python's C API to interact with the
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core and with user code.
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file object
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An object exposing a file-oriented API (with methods such as
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:meth:`read()` or :meth:`write()`) to an underlying resource. Depending
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on the way it was created, a file object can mediate access to a real
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on-disk file or to another type of storage or communication device
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(for example standard input/output, in-memory buffers, sockets, pipes,
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etc.). File objects are also called :dfn:`file-like objects` or
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:dfn:`streams`.
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There are actually three categories of file objects: raw
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:term:`binary files <binary file>`, buffered
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:term:`binary files <binary file>` and :term:`text files <text file>`.
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Their interfaces are defined in the :mod:`io` module. The canonical
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way to create a file object is by using the :func:`open` function.
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file-like object
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A synonym for :term:`file object`.
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finder
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An object that tries to find the :term:`loader` for a module. It must
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implement either a method named :meth:`find_loader` or a method named
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:meth:`find_module`. See :pep:`302` and :pep:`420` for details and
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:class:`importlib.abc.Finder` for an :term:`abstract base class`.
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floor division
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Mathematical division that rounds down to nearest integer. The floor
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division operator is ``//``. For example, the expression ``11 // 4``
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evaluates to ``2`` in contrast to the ``2.75`` returned by float true
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division. Note that ``(-11) // 4`` is ``-3`` because that is ``-2.75``
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rounded *downward*. See :pep:`238`.
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function
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A series of statements which returns some value to a caller. It can also
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be passed zero or more :term:`arguments <argument>` which may be used in
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the execution of the body. See also :term:`parameter`, :term:`method`,
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and the :ref:`function` section.
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function annotation
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An arbitrary metadata value associated with a function parameter or return
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value. Its syntax is explained in section :ref:`function`. Annotations
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may be accessed via the :attr:`__annotations__` special attribute of a
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function object.
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Python itself does not assign any particular meaning to function
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annotations. They are intended to be interpreted by third-party libraries
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or tools. See :pep:`3107`, which describes some of their potential uses.
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__future__
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A pseudo-module which programmers can use to enable new language features
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which are not compatible with the current interpreter.
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By importing the :mod:`__future__` module and evaluating its variables,
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you can see when a new feature was first added to the language and when it
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becomes the default::
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>>> import __future__
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>>> __future__.division
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_Feature((2, 2, 0, 'alpha', 2), (3, 0, 0, 'alpha', 0), 8192)
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garbage collection
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The process of freeing memory when it is not used anymore. Python
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performs garbage collection via reference counting and a cyclic garbage
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collector that is able to detect and break reference cycles.
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.. index:: single: generator
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generator
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A function which returns an iterator. It looks like a normal function
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except that it contains :keyword:`yield` statements for producing a series
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a values usable in a for-loop or that can be retrieved one at a time with
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the :func:`next` function. Each :keyword:`yield` temporarily suspends
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processing, remembering the location execution state (including local
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variables and pending try-statements). When the generator resumes, it
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picks-up where it left-off (in contrast to functions which start fresh on
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every invocation).
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.. index:: single: generator expression
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generator expression
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An expression that returns an iterator. It looks like a normal expression
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followed by a :keyword:`for` expression defining a loop variable, range,
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and an optional :keyword:`if` expression. The combined expression
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generates values for an enclosing function::
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>>> sum(i*i for i in range(10)) # sum of squares 0, 1, 4, ... 81
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285
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GIL
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See :term:`global interpreter lock`.
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global interpreter lock
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The mechanism used by the :term:`CPython` interpreter to assure that
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only one thread executes Python :term:`bytecode` at a time.
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This simplifies the CPython implementation by making the object model
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(including critical built-in types such as :class:`dict`) implicitly
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safe against concurrent access. Locking the entire interpreter
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makes it easier for the interpreter to be multi-threaded, at the
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expense of much of the parallelism afforded by multi-processor
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machines.
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However, some extension modules, either standard or third-party,
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are designed so as to release the GIL when doing computationally-intensive
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tasks such as compression or hashing. Also, the GIL is always released
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when doing I/O.
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Past efforts to create a "free-threaded" interpreter (one which locks
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shared data at a much finer granularity) have not been successful
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because performance suffered in the common single-processor case. It
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is believed that overcoming this performance issue would make the
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implementation much more complicated and therefore costlier to maintain.
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hashable
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An object is *hashable* if it has a hash value which never changes during
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its lifetime (it needs a :meth:`__hash__` method), and can be compared to
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other objects (it needs an :meth:`__eq__` method). Hashable objects which
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compare equal must have the same hash value.
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Hashability makes an object usable as a dictionary key and a set member,
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because these data structures use the hash value internally.
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All of Python's immutable built-in objects are hashable, while no mutable
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containers (such as lists or dictionaries) are. Objects which are
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instances of user-defined classes are hashable by default; they all
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compare unequal (except with themselves), and their hash value is their
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:func:`id`.
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IDLE
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An Integrated Development Environment for Python. IDLE is a basic editor
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and interpreter environment which ships with the standard distribution of
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Python.
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immutable
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An object with a fixed value. Immutable objects include numbers, strings and
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tuples. Such an object cannot be altered. A new object has to
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be created if a different value has to be stored. They play an important
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role in places where a constant hash value is needed, for example as a key
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in a dictionary.
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import path
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A list of locations (or :term:`path entries <path entry>`) that are
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searched by the :term:`path based finder` for modules to import. During
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import, this list of locations usually comes from :data:`sys.path`, but
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for subpackages it may also come from the parent package's ``__path__``
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attribute.
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importing
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The process by which Python code in one module is made available to
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Python code in another module.
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importer
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An object that both finds and loads a module; both a
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:term:`finder` and :term:`loader` object.
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interactive
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Python has an interactive interpreter which means you can enter
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statements and expressions at the interpreter prompt, immediately
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execute them and see their results. Just launch ``python`` with no
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arguments (possibly by selecting it from your computer's main
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menu). It is a very powerful way to test out new ideas or inspect
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modules and packages (remember ``help(x)``).
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interpreted
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Python is an interpreted language, as opposed to a compiled one,
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though the distinction can be blurry because of the presence of the
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bytecode compiler. This means that source files can be run directly
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without explicitly creating an executable which is then run.
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Interpreted languages typically have a shorter development/debug cycle
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than compiled ones, though their programs generally also run more
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slowly. See also :term:`interactive`.
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iterable
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An object capable of returning its members one at a time. Examples of
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iterables include all sequence types (such as :class:`list`, :class:`str`,
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and :class:`tuple`) and some non-sequence types like :class:`dict`,
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:term:`file objects <file object>`, and objects of any classes you define
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with an :meth:`__iter__` or :meth:`__getitem__` method. Iterables can be
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used in a :keyword:`for` loop and in many other places where a sequence is
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needed (:func:`zip`, :func:`map`, ...). When an iterable object is passed
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as an argument to the built-in function :func:`iter`, it returns an
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iterator for the object. This iterator is good for one pass over the set
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of values. When using iterables, it is usually not necessary to call
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:func:`iter` or deal with iterator objects yourself. The ``for``
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statement does that automatically for you, creating a temporary unnamed
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variable to hold the iterator for the duration of the loop. See also
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:term:`iterator`, :term:`sequence`, and :term:`generator`.
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iterator
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An object representing a stream of data. Repeated calls to the iterator's
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:meth:`~iterator.__next__` method (or passing it to the built-in function
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:func:`next`) return successive items in the stream. When no more data
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are available a :exc:`StopIteration` exception is raised instead. At this
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point, the iterator object is exhausted and any further calls to its
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|
:meth:`__next__` method just raise :exc:`StopIteration` again. Iterators
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|
are required to have an :meth:`__iter__` method that returns the iterator
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object itself so every iterator is also iterable and may be used in most
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places where other iterables are accepted. One notable exception is code
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which attempts multiple iteration passes. A container object (such as a
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:class:`list`) produces a fresh new iterator each time you pass it to the
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:func:`iter` function or use it in a :keyword:`for` loop. Attempting this
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with an iterator will just return the same exhausted iterator object used
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in the previous iteration pass, making it appear like an empty container.
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More information can be found in :ref:`typeiter`.
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key function
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A key function or collation function is a callable that returns a value
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used for sorting or ordering. For example, :func:`locale.strxfrm` is
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used to produce a sort key that is aware of locale specific sort
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conventions.
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A number of tools in Python accept key functions to control how elements
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are ordered or grouped. They include :func:`min`, :func:`max`,
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:func:`sorted`, :meth:`list.sort`, :func:`heapq.nsmallest`,
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:func:`heapq.nlargest`, and :func:`itertools.groupby`.
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There are several ways to create a key function. For example. the
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:meth:`str.lower` method can serve as a key function for case insensitive
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sorts. Alternatively, an ad-hoc key function can be built from a
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:keyword:`lambda` expression such as ``lambda r: (r[0], r[2])``. Also,
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the :mod:`operator` module provides three key function constructors:
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:func:`~operator.attrgetter`, :func:`~operator.itemgetter`, and
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:func:`~operator.methodcaller`. See the :ref:`Sorting HOW TO
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<sortinghowto>` for examples of how to create and use key functions.
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keyword argument
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See :term:`argument`.
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lambda
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An anonymous inline function consisting of a single :term:`expression`
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|
which is evaluated when the function is called. The syntax to create
|
|
a lambda function is ``lambda [arguments]: expression``
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LBYL
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|
Look before you leap. This coding style explicitly tests for
|
|
pre-conditions before making calls or lookups. This style contrasts with
|
|
the :term:`EAFP` approach and is characterized by the presence of many
|
|
:keyword:`if` statements.
|
|
|
|
In a multi-threaded environment, the LBYL approach can risk introducing a
|
|
race condition between "the looking" and "the leaping". For example, the
|
|
code, ``if key in mapping: return mapping[key]`` can fail if another
|
|
thread removes *key* from *mapping* after the test, but before the lookup.
|
|
This issue can be solved with locks or by using the EAFP approach.
|
|
|
|
list
|
|
A built-in Python :term:`sequence`. Despite its name it is more akin
|
|
to an array in other languages than to a linked list since access to
|
|
elements are O(1).
|
|
|
|
list comprehension
|
|
A compact way to process all or part of the elements in a sequence and
|
|
return a list with the results. ``result = ['{:#04x}'.format(x) for x in
|
|
range(256) if x % 2 == 0]`` generates a list of strings containing
|
|
even hex numbers (0x..) in the range from 0 to 255. The :keyword:`if`
|
|
clause is optional. If omitted, all elements in ``range(256)`` are
|
|
processed.
|
|
|
|
loader
|
|
An object that loads a module. It must define a method named
|
|
:meth:`load_module`. A loader is typically returned by a
|
|
:term:`finder`. See :pep:`302` for details and
|
|
:class:`importlib.abc.Loader` for an :term:`abstract base class`.
|
|
|
|
mapping
|
|
A container object that supports arbitrary key lookups and implements the
|
|
methods specified in the :class:`~collections.abc.Mapping` or
|
|
:class:`~collections.abc.MutableMapping`
|
|
:ref:`abstract base classes <collections-abstract-base-classes>`. Examples
|
|
include :class:`dict`, :class:`collections.defaultdict`,
|
|
:class:`collections.OrderedDict` and :class:`collections.Counter`.
|
|
|
|
meta path finder
|
|
A finder returned by a search of :data:`sys.meta_path`. Meta path
|
|
finders are related to, but different from :term:`path entry finders
|
|
<path entry finder>`.
|
|
|
|
metaclass
|
|
The class of a class. Class definitions create a class name, a class
|
|
dictionary, and a list of base classes. The metaclass is responsible for
|
|
taking those three arguments and creating the class. Most object oriented
|
|
programming languages provide a default implementation. What makes Python
|
|
special is that it is possible to create custom metaclasses. Most users
|
|
never need this tool, but when the need arises, metaclasses can provide
|
|
powerful, elegant solutions. They have been used for logging attribute
|
|
access, adding thread-safety, tracking object creation, implementing
|
|
singletons, and many other tasks.
|
|
|
|
More information can be found in :ref:`metaclasses`.
|
|
|
|
method
|
|
A function which is defined inside a class body. If called as an attribute
|
|
of an instance of that class, the method will get the instance object as
|
|
its first :term:`argument` (which is usually called ``self``).
|
|
See :term:`function` and :term:`nested scope`.
|
|
|
|
method resolution order
|
|
Method Resolution Order is the order in which base classes are searched
|
|
for a member during lookup. See `The Python 2.3 Method Resolution Order
|
|
<http://www.python.org/download/releases/2.3/mro/>`_.
|
|
|
|
module
|
|
An object that serves as an organizational unit of Python code. Modules
|
|
have a namespace containing arbitrary Python objects. Modules are loaded
|
|
into Python by the process of :term:`importing`.
|
|
|
|
See also :term:`package`.
|
|
|
|
MRO
|
|
See :term:`method resolution order`.
|
|
|
|
mutable
|
|
Mutable objects can change their value but keep their :func:`id`. See
|
|
also :term:`immutable`.
|
|
|
|
named tuple
|
|
Any tuple-like class whose indexable elements are also accessible using
|
|
named attributes (for example, :func:`time.localtime` returns a
|
|
tuple-like object where the *year* is accessible either with an
|
|
index such as ``t[0]`` or with a named attribute like ``t.tm_year``).
|
|
|
|
A named tuple can be a built-in type such as :class:`time.struct_time`,
|
|
or it can be created with a regular class definition. A full featured
|
|
named tuple can also be created with the factory function
|
|
:func:`collections.namedtuple`. The latter approach automatically
|
|
provides extra features such as a self-documenting representation like
|
|
``Employee(name='jones', title='programmer')``.
|
|
|
|
namespace
|
|
The place where a variable is stored. Namespaces are implemented as
|
|
dictionaries. There are the local, global and built-in namespaces as well
|
|
as nested namespaces in objects (in methods). Namespaces support
|
|
modularity by preventing naming conflicts. For instance, the functions
|
|
:func:`builtins.open <.open>` and :func:`os.open` are distinguished by
|
|
their namespaces. Namespaces also aid readability and maintainability by
|
|
making it clear which module implements a function. For instance, writing
|
|
:func:`random.seed` or :func:`itertools.islice` makes it clear that those
|
|
functions are implemented by the :mod:`random` and :mod:`itertools`
|
|
modules, respectively.
|
|
|
|
namespace package
|
|
A :pep:`420` :term:`package` which serves only as a container for
|
|
subpackages. Namespace packages may have no physical representation,
|
|
and specifically are not like a :term:`regular package` because they
|
|
have no ``__init__.py`` file.
|
|
|
|
See also :term:`module`.
|
|
|
|
nested scope
|
|
The ability to refer to a variable in an enclosing definition. For
|
|
instance, a function defined inside another function can refer to
|
|
variables in the outer function. Note that nested scopes by default work
|
|
only for reference and not for assignment. Local variables both read and
|
|
write in the innermost scope. Likewise, global variables read and write
|
|
to the global namespace. The :keyword:`nonlocal` allows writing to outer
|
|
scopes.
|
|
|
|
new-style class
|
|
Old name for the flavor of classes now used for all class objects. In
|
|
earlier Python versions, only new-style classes could use Python's newer,
|
|
versatile features like :attr:`~object.__slots__`, descriptors,
|
|
properties, :meth:`__getattribute__`, class methods, and static methods.
|
|
|
|
object
|
|
Any data with state (attributes or value) and defined behavior
|
|
(methods). Also the ultimate base class of any :term:`new-style
|
|
class`.
|
|
|
|
package
|
|
A Python :term:`module` which can contain submodules or recursively,
|
|
subpackages. Technically, a package is a Python module with an
|
|
``__path__`` attribute.
|
|
|
|
See also :term:`regular package` and :term:`namespace package`.
|
|
|
|
parameter
|
|
A named entity in a :term:`function` (or method) definition that
|
|
specifies an :term:`argument` (or in some cases, arguments) that the
|
|
function can accept. There are five kinds of parameter:
|
|
|
|
* :dfn:`positional-or-keyword`: specifies an argument that can be passed
|
|
either :term:`positionally <argument>` or as a :term:`keyword argument
|
|
<argument>`. This is the default kind of parameter, for example *foo*
|
|
and *bar* in the following::
|
|
|
|
def func(foo, bar=None): ...
|
|
|
|
* :dfn:`positional-only`: specifies an argument that can be supplied only
|
|
by position. Python has no syntax for defining positional-only
|
|
parameters. However, some built-in functions have positional-only
|
|
parameters (e.g. :func:`abs`).
|
|
|
|
.. _keyword-only_parameter:
|
|
|
|
* :dfn:`keyword-only`: specifies an argument that can be supplied only
|
|
by keyword. Keyword-only parameters can be defined by including a
|
|
single var-positional parameter or bare ``*`` in the parameter list
|
|
of the function definition before them, for example *kw_only1* and
|
|
*kw_only2* in the following::
|
|
|
|
def func(arg, *, kw_only1, kw_only2): ...
|
|
|
|
* :dfn:`var-positional`: specifies that an arbitrary sequence of
|
|
positional arguments can be provided (in addition to any positional
|
|
arguments already accepted by other parameters). Such a parameter can
|
|
be defined by prepending the parameter name with ``*``, for example
|
|
*args* in the following::
|
|
|
|
def func(*args, **kwargs): ...
|
|
|
|
* :dfn:`var-keyword`: specifies that arbitrarily many keyword arguments
|
|
can be provided (in addition to any keyword arguments already accepted
|
|
by other parameters). Such a parameter can be defined by prepending
|
|
the parameter name with ``**``, for example *kwargs* in the example
|
|
above.
|
|
|
|
Parameters can specify both optional and required arguments, as well as
|
|
default values for some optional arguments.
|
|
|
|
See also the :term:`argument` glossary entry, the FAQ question on
|
|
:ref:`the difference between arguments and parameters
|
|
<faq-argument-vs-parameter>`, the :class:`inspect.Parameter` class, the
|
|
:ref:`function` section, and :pep:`362`.
|
|
|
|
path entry
|
|
A single location on the :term:`import path` which the :term:`path
|
|
based finder` consults to find modules for importing.
|
|
|
|
path entry finder
|
|
A :term:`finder` returned by a callable on :data:`sys.path_hooks`
|
|
(i.e. a :term:`path entry hook`) which knows how to locate modules given
|
|
a :term:`path entry`.
|
|
|
|
path entry hook
|
|
A callable on the :data:`sys.path_hook` list which returns a :term:`path
|
|
entry finder` if it knows how to find modules on a specific :term:`path
|
|
entry`.
|
|
|
|
path based finder
|
|
One of the default :term:`meta path finders <meta path finder>` which
|
|
searches an :term:`import path` for modules.
|
|
|
|
portion
|
|
A set of files in a single directory (possibly stored in a zip file)
|
|
that contribute to a namespace package, as defined in :pep:`420`.
|
|
|
|
positional argument
|
|
See :term:`argument`.
|
|
|
|
provisional package
|
|
A provisional package is one which has been deliberately excluded from
|
|
the standard library's backwards compatibility guarantees. While major
|
|
changes to such packages are not expected, as long as they are marked
|
|
provisional, backwards incompatible changes (up to and including removal
|
|
of the package) may occur if deemed necessary by core developers. Such
|
|
changes will not be made gratuitously -- they will occur only if serious
|
|
flaws are uncovered that were missed prior to the inclusion of the
|
|
package.
|
|
|
|
This process allows the standard library to continue to evolve over
|
|
time, without locking in problematic design errors for extended periods
|
|
of time. See :pep:`411` for more details.
|
|
|
|
Python 3000
|
|
Nickname for the Python 3.x release line (coined long ago when the
|
|
release of version 3 was something in the distant future.) This is also
|
|
abbreviated "Py3k".
|
|
|
|
Pythonic
|
|
An idea or piece of code which closely follows the most common idioms
|
|
of the Python language, rather than implementing code using concepts
|
|
common to other languages. For example, a common idiom in Python is
|
|
to loop over all elements of an iterable using a :keyword:`for`
|
|
statement. Many other languages don't have this type of construct, so
|
|
people unfamiliar with Python sometimes use a numerical counter instead::
|
|
|
|
for i in range(len(food)):
|
|
print(food[i])
|
|
|
|
As opposed to the cleaner, Pythonic method::
|
|
|
|
for piece in food:
|
|
print(piece)
|
|
|
|
qualified name
|
|
A dotted name showing the "path" from a module's global scope to a
|
|
class, function or method defined in that module, as defined in
|
|
:pep:`3155`. For top-level functions and classes, the qualified name
|
|
is the same as the object's name::
|
|
|
|
>>> class C:
|
|
... class D:
|
|
... def meth(self):
|
|
... pass
|
|
...
|
|
>>> C.__qualname__
|
|
'C'
|
|
>>> C.D.__qualname__
|
|
'C.D'
|
|
>>> C.D.meth.__qualname__
|
|
'C.D.meth'
|
|
|
|
When used to refer to modules, the *fully qualified name* means the
|
|
entire dotted path to the module, including any parent packages,
|
|
e.g. ``email.mime.text``::
|
|
|
|
>>> import email.mime.text
|
|
>>> email.mime.text.__name__
|
|
'email.mime.text'
|
|
|
|
reference count
|
|
The number of references to an object. When the reference count of an
|
|
object drops to zero, it is deallocated. Reference counting is
|
|
generally not visible to Python code, but it is a key element of the
|
|
:term:`CPython` implementation. The :mod:`sys` module defines a
|
|
:func:`~sys.getrefcount` function that programmers can call to return the
|
|
reference count for a particular object.
|
|
|
|
regular package
|
|
A traditional :term:`package`, such as a directory containing an
|
|
``__init__.py`` file.
|
|
|
|
See also :term:`namespace package`.
|
|
|
|
__slots__
|
|
A declaration inside a class that saves memory by pre-declaring space for
|
|
instance attributes and eliminating instance dictionaries. Though
|
|
popular, the technique is somewhat tricky to get right and is best
|
|
reserved for rare cases where there are large numbers of instances in a
|
|
memory-critical application.
|
|
|
|
sequence
|
|
An :term:`iterable` which supports efficient element access using integer
|
|
indices via the :meth:`__getitem__` special method and defines a
|
|
:meth:`__len__` method that returns the length of the sequence.
|
|
Some built-in sequence types are :class:`list`, :class:`str`,
|
|
:class:`tuple`, and :class:`bytes`. Note that :class:`dict` also
|
|
supports :meth:`__getitem__` and :meth:`__len__`, but is considered a
|
|
mapping rather than a sequence because the lookups use arbitrary
|
|
:term:`immutable` keys rather than integers.
|
|
|
|
The :class:`collections.abc.Sequence` abstract base class
|
|
defines a much richer interface that goes beyond just
|
|
:meth:`__getitem__` and :meth:`__len__`, adding :meth:`count`,
|
|
:meth:`index`, :meth:`__contains__`, and
|
|
:meth:`__reversed__`. Types that implement this expanded
|
|
interface can be registered explicitly using
|
|
:func:`~abc.register`.
|
|
|
|
slice
|
|
An object usually containing a portion of a :term:`sequence`. A slice is
|
|
created using the subscript notation, ``[]`` with colons between numbers
|
|
when several are given, such as in ``variable_name[1:3:5]``. The bracket
|
|
(subscript) notation uses :class:`slice` objects internally.
|
|
|
|
special method
|
|
A method that is called implicitly by Python to execute a certain
|
|
operation on a type, such as addition. Such methods have names starting
|
|
and ending with double underscores. Special methods are documented in
|
|
:ref:`specialnames`.
|
|
|
|
statement
|
|
A statement is part of a suite (a "block" of code). A statement is either
|
|
an :term:`expression` or one of several constructs with a keyword, such
|
|
as :keyword:`if`, :keyword:`while` or :keyword:`for`.
|
|
|
|
struct sequence
|
|
A tuple with named elements. Struct sequences expose an interface similar
|
|
to :term:`named tuple` in that elements can either be accessed either by
|
|
index or as an attribute. However, they do not have any of the named tuple
|
|
methods like :meth:`~collections.somenamedtuple._make` or
|
|
:meth:`~collections.somenamedtuple._asdict`. Examples of struct sequences
|
|
include :data:`sys.float_info` and the return value of :func:`os.stat`.
|
|
|
|
text file
|
|
A :term:`file object` able to read and write :class:`str` objects.
|
|
Often, a text file actually accesses a byte-oriented datastream
|
|
and handles the text encoding automatically.
|
|
|
|
.. seealso::
|
|
A :term:`binary file` reads and write :class:`bytes` objects.
|
|
|
|
triple-quoted string
|
|
A string which is bound by three instances of either a quotation mark
|
|
(") or an apostrophe ('). While they don't provide any functionality
|
|
not available with single-quoted strings, they are useful for a number
|
|
of reasons. They allow you to include unescaped single and double
|
|
quotes within a string and they can span multiple lines without the
|
|
use of the continuation character, making them especially useful when
|
|
writing docstrings.
|
|
|
|
type
|
|
The type of a Python object determines what kind of object it is; every
|
|
object has a type. An object's type is accessible as its
|
|
:attr:`~instance.__class__` attribute or can be retrieved with
|
|
``type(obj)``.
|
|
|
|
universal newlines
|
|
A manner of interpreting text streams in which all of the following are
|
|
recognized as ending a line: the Unix end-of-line convention ``'\n'``,
|
|
the Windows convention ``'\r\n'``, and the old Macintosh convention
|
|
``'\r'``. See :pep:`278` and :pep:`3116`, as well as
|
|
:func:`str.splitlines` for an additional use.
|
|
|
|
view
|
|
The objects returned from :meth:`dict.keys`, :meth:`dict.values`, and
|
|
:meth:`dict.items` are called dictionary views. They are lazy sequences
|
|
that will see changes in the underlying dictionary. To force the
|
|
dictionary view to become a full list use ``list(dictview)``. See
|
|
:ref:`dict-views`.
|
|
|
|
virtual machine
|
|
A computer defined entirely in software. Python's virtual machine
|
|
executes the :term:`bytecode` emitted by the bytecode compiler.
|
|
|
|
Zen of Python
|
|
Listing of Python design principles and philosophies that are helpful in
|
|
understanding and using the language. The listing can be found by typing
|
|
"``import this``" at the interactive prompt.
|