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PEP 683 (immortal objects) revealed some ways in which the Python documentation has been unnecessarily coupled to the implementation details of reference counts. In the end users should focus on reference ownership, including taking references and releasing them, rather than on how many reference counts an object has. This change updates the documentation to reflect that perspective. It also updates the docs relative to immortal objects in a handful of places.
1270 lines
57 KiB
ReStructuredText
1270 lines
57 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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Can refer to:
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* The default Python prompt of the interactive shell when entering the
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code for an indented code block, when within a pair of matching left and
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right delimiters (parentheses, square brackets, curly braces or triple
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quotes), or after specifying a decorator.
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* The :const:`Ellipsis` built-in constant.
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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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annotation
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A label associated with a variable, a class
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attribute or a function parameter or return value,
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used by convention as a :term:`type hint`.
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Annotations of local variables cannot be accessed at runtime, but
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annotations of global variables, class attributes, and functions
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are stored in the :attr:`__annotations__`
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special attribute of modules, classes, and functions,
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respectively.
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See :term:`variable annotation`, :term:`function annotation`, :pep:`484`
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and :pep:`526`, which describe this functionality.
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Also see :ref:`annotations-howto`
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for best practices on working with annotations.
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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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asynchronous context manager
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An object which controls the environment seen in an
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:keyword:`async with` statement by defining :meth:`~object.__aenter__` and
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:meth:`~object.__aexit__` methods. Introduced by :pep:`492`.
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asynchronous generator
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A function which returns an :term:`asynchronous generator iterator`. It
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looks like a coroutine function defined with :keyword:`async def` except
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that it contains :keyword:`yield` expressions for producing a series of
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values usable in an :keyword:`async for` loop.
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Usually refers to an asynchronous generator function, but may refer to an
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*asynchronous generator iterator* in some contexts. In cases where the
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intended meaning isn't clear, using the full terms avoids ambiguity.
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An asynchronous generator function may contain :keyword:`await`
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expressions as well as :keyword:`async for`, and :keyword:`async with`
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statements.
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asynchronous generator iterator
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An object created by a :term:`asynchronous generator` function.
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This is an :term:`asynchronous iterator` which when called using the
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:meth:`~object.__anext__` method returns an awaitable object which will execute
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the body of the asynchronous generator function until the next
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:keyword:`yield` expression.
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Each :keyword:`yield` temporarily suspends processing, remembering the
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location execution state (including local variables and pending
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try-statements). When the *asynchronous generator iterator* effectively
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resumes with another awaitable returned by :meth:`~object.__anext__`, it
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picks up where it left off. See :pep:`492` and :pep:`525`.
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asynchronous iterable
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An object, that can be used in an :keyword:`async for` statement.
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Must return an :term:`asynchronous iterator` from its
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:meth:`~object.__aiter__` method. Introduced by :pep:`492`.
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asynchronous iterator
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An object that implements the :meth:`~object.__aiter__` and :meth:`~object.__anext__`
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methods. :meth:`~object.__anext__` must return an :term:`awaitable` object.
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:keyword:`async for` resolves the awaitables returned by an asynchronous
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iterator's :meth:`~object.__anext__` method until it raises a
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:exc:`StopAsyncIteration` exception. Introduced by :pep:`492`.
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attribute
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A value associated with an object which is usually referenced by name
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using dotted expressions.
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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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It is possible to give an object an attribute whose name is not an
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identifier as defined by :ref:`identifiers`, for example using
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:func:`setattr`, if the object allows it.
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Such an attribute will not be accessible using a dotted expression,
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and would instead need to be retrieved with :func:`getattr`.
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awaitable
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An object that can be used in an :keyword:`await` expression. Can be
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a :term:`coroutine` or an object with an :meth:`~object.__await__` method.
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See also :pep:`492`.
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BDFL
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Benevolent Dictator For Life, a.k.a. `Guido van Rossum
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<https://gvanrossum.github.io/>`_, 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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Examples of binary files are files opened in binary mode (``'rb'``,
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``'wb'`` or ``'rb+'``), :data:`sys.stdin.buffer`,
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:data:`sys.stdout.buffer`, and instances of :class:`io.BytesIO` and
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:class:`gzip.GzipFile`.
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See also :term:`text file` for a file object able to read and write
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:class:`str` objects.
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borrowed reference
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In Python's C API, a borrowed reference is a reference to an object,
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where the code using the object does not own the reference.
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It becomes a dangling
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pointer if the object is destroyed. For example, a garbage collection can
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remove the last :term:`strong reference` to the object and so destroy it.
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Calling :c:func:`Py_INCREF` on the :term:`borrowed reference` is
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recommended to convert it to a :term:`strong reference` in-place, except
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when the object cannot be destroyed before the last usage of the borrowed
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reference. The :c:func:`Py_NewRef` function can be used to create a new
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:term:`strong reference`.
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bytes-like object
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An object that supports the :ref:`bufferobjects` and can
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export a C-:term:`contiguous` buffer. This includes all :class:`bytes`,
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:class:`bytearray`, and :class:`array.array` objects, as well as many
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common :class:`memoryview` objects. Bytes-like objects can
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be used for various operations that work with binary data; these include
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compression, saving to a binary file, and sending over a socket.
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Some operations need the binary data to be mutable. The documentation
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often refers to these as "read-write bytes-like objects". Example
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mutable buffer objects include :class:`bytearray` and a
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:class:`memoryview` of a :class:`bytearray`.
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Other operations require the binary data to be stored in
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immutable objects ("read-only bytes-like objects"); examples
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of these include :class:`bytes` and a :class:`memoryview`
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of a :class:`bytes` object.
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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`` 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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callable
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A callable is an object that can be called, possibly with a set
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of arguments (see :term:`argument`), with the following syntax::
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callable(argument1, argument2, argumentN)
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A :term:`function`, and by extension a :term:`method`, is a callable.
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An instance of a class that implements the :meth:`~object.__call__`
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method is also a callable.
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callback
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A subroutine function which is passed as an argument to be executed at
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some point in the future.
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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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class variable
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A variable defined in a class and intended to be modified only at
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class level (i.e., not in an instance of the class).
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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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context variable
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A variable which can have different values depending on its context.
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This is similar to Thread-Local Storage in which each execution
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thread may have a different value for a variable. However, with context
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variables, there may be several contexts in one execution thread and the
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main usage for context variables is to keep track of variables in
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concurrent asynchronous tasks.
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See :mod:`contextvars`.
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contiguous
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.. index:: C-contiguous, Fortran contiguous
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A buffer is considered contiguous exactly if it is either
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*C-contiguous* or *Fortran contiguous*. Zero-dimensional buffers are
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C and Fortran contiguous. In one-dimensional arrays, the items
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must be laid out in memory next to each other, in order of
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increasing indexes starting from zero. In multidimensional
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C-contiguous arrays, the last index varies the fastest when
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visiting items in order of memory address. However, in
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Fortran contiguous arrays, the first index varies the fastest.
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coroutine
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Coroutines are a more generalized form of subroutines. Subroutines are
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entered at one point and exited at another point. Coroutines can be
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entered, exited, and resumed at many different points. They can be
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implemented with the :keyword:`async def` statement. See also
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:pep:`492`.
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coroutine function
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A function which returns a :term:`coroutine` object. A coroutine
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function may be defined with the :keyword:`async def` statement,
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and may contain :keyword:`await`, :keyword:`async for`, and
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:keyword:`async with` keywords. These were introduced
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by :pep:`492`.
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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 <https://www.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(arg):
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...
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f = staticmethod(f)
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@staticmethod
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def f(arg):
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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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or the :ref:`Descriptor How To Guide <descriptorhowto>`.
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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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dictionary comprehension
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A compact way to process all or part of the elements in an iterable and
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return a dictionary with the results. ``results = {n: n ** 2 for n in
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range(10)}`` generates a dictionary containing key ``n`` mapped to
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value ``n ** 2``. See :ref:`comprehensions`.
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dictionary view
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The objects returned from :meth:`dict.keys`, :meth:`dict.values`, and
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:meth:`dict.items` are called dictionary views. They provide a dynamic
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view on the dictionary’s entries, which means that when the dictionary
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changes, the view reflects these changes. To force the
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dictionary view to become a full list use ``list(dictview)``. See
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:ref:`dict-views`.
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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:`while`. 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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f-string
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String literals prefixed with ``'f'`` or ``'F'`` are commonly called
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"f-strings" which is short for
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:ref:`formatted string literals <f-strings>`. See also :pep:`498`.
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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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filesystem encoding and error handler
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Encoding and error handler used by Python to decode bytes from the
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operating system and encode Unicode to the operating system.
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The filesystem encoding must guarantee to successfully decode all bytes
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below 128. If the file system encoding fails to provide this guarantee,
|
||
API functions can raise :exc:`UnicodeError`.
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||
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The :func:`sys.getfilesystemencoding` and
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||
:func:`sys.getfilesystemencodeerrors` functions can be used to get the
|
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filesystem encoding and error handler.
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||
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The :term:`filesystem encoding and error handler` are configured at
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Python startup by the :c:func:`PyConfig_Read` function: see
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||
:c:member:`~PyConfig.filesystem_encoding` and
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:c:member:`~PyConfig.filesystem_errors` members of :c:type:`PyConfig`.
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||
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See also the :term:`locale encoding`.
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||
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||
finder
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||
An object that tries to find the :term:`loader` for a module that is
|
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being imported.
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||
|
||
Since Python 3.3, there are two types of finder: :term:`meta path finders
|
||
<meta path finder>` for use with :data:`sys.meta_path`, and :term:`path
|
||
entry finders <path entry finder>` for use with :data:`sys.path_hooks`.
|
||
|
||
See :pep:`302`, :pep:`420` and :pep:`451` for much more detail.
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floor division
|
||
Mathematical division that rounds down to nearest integer. The floor
|
||
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
|
||
A series of statements which returns some value to a caller. It can also
|
||
be passed zero or more :term:`arguments <argument>` which may be used in
|
||
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
|
||
An :term:`annotation` of a function parameter or return value.
|
||
|
||
Function annotations are usually used for
|
||
:term:`type hints <type hint>`: for example, this function is expected to take two
|
||
:class:`int` arguments and is also expected to have an :class:`int`
|
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return value::
|
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|
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def sum_two_numbers(a: int, b: int) -> int:
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return a + b
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|
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Function annotation syntax is explained in section :ref:`function`.
|
||
|
||
See :term:`variable annotation` and :pep:`484`,
|
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which describe this functionality.
|
||
Also see :ref:`annotations-howto`
|
||
for best practices on working with annotations.
|
||
|
||
__future__
|
||
A :ref:`future statement <future>`, ``from __future__ import <feature>``,
|
||
directs the compiler to compile the current module using syntax or
|
||
semantics that will become standard in a future release of Python.
|
||
The :mod:`__future__` module documents the possible values of
|
||
*feature*. By importing this module and evaluating its variables,
|
||
you can see when a new feature was first added to the language and
|
||
when it will (or did) become the default::
|
||
|
||
>>> import __future__
|
||
>>> __future__.division
|
||
_Feature((2, 2, 0, 'alpha', 2), (3, 0, 0, 'alpha', 0), 8192)
|
||
|
||
garbage collection
|
||
The process of freeing memory when it is not used anymore. Python
|
||
performs garbage collection via reference counting and a cyclic garbage
|
||
collector that is able to detect and break reference cycles. The
|
||
garbage collector can be controlled using the :mod:`gc` module.
|
||
|
||
.. index:: single: generator
|
||
|
||
generator
|
||
A function which returns a :term:`generator iterator`. It looks like a
|
||
normal function except that it contains :keyword:`yield` expressions
|
||
for producing a series of values usable in a for-loop or that can be
|
||
retrieved one at a time with the :func:`next` function.
|
||
|
||
Usually refers to a generator function, but may refer to a
|
||
*generator iterator* in some contexts. In cases where the intended
|
||
meaning isn't clear, using the full terms avoids ambiguity.
|
||
|
||
generator iterator
|
||
An object created by a :term:`generator` function.
|
||
|
||
Each :keyword:`yield` temporarily suspends processing, remembering the
|
||
location execution state (including local variables and pending
|
||
try-statements). When the *generator iterator* resumes, it picks up where
|
||
it left off (in contrast to functions which start fresh on every
|
||
invocation).
|
||
|
||
.. index:: single: generator expression
|
||
|
||
generator expression
|
||
An expression that returns an iterator. It looks like a normal expression
|
||
followed by a :keyword:`!for` clause defining a loop variable, range,
|
||
and an optional :keyword:`!if` clause. The combined expression
|
||
generates values for an enclosing function::
|
||
|
||
>>> sum(i*i for i in range(10)) # sum of squares 0, 1, 4, ... 81
|
||
285
|
||
|
||
generic function
|
||
A function composed of multiple functions implementing the same operation
|
||
for different types. Which implementation should be used during a call is
|
||
determined by the dispatch algorithm.
|
||
|
||
See also the :term:`single dispatch` glossary entry, the
|
||
:func:`functools.singledispatch` decorator, and :pep:`443`.
|
||
|
||
generic type
|
||
A :term:`type` that can be parameterized; typically a
|
||
:ref:`container class<sequence-types>` such as :class:`list` or
|
||
:class:`dict`. Used for :term:`type hints <type hint>` and
|
||
:term:`annotations <annotation>`.
|
||
|
||
For more details, see :ref:`generic alias types<types-genericalias>`,
|
||
:pep:`483`, :pep:`484`, :pep:`585`, and the :mod:`typing` module.
|
||
|
||
GIL
|
||
See :term:`global interpreter lock`.
|
||
|
||
global interpreter lock
|
||
The mechanism used by the :term:`CPython` interpreter to assure that
|
||
only one thread executes Python :term:`bytecode` at a time.
|
||
This simplifies the CPython implementation by making the object model
|
||
(including critical built-in types such as :class:`dict`) implicitly
|
||
safe against concurrent access. Locking the entire interpreter
|
||
makes it easier for the interpreter to be multi-threaded, at the
|
||
expense of much of the parallelism afforded by multi-processor
|
||
machines.
|
||
|
||
However, some extension modules, either standard or third-party,
|
||
are designed so as to release the GIL when doing computationally intensive
|
||
tasks such as compression or hashing. Also, the GIL is always released
|
||
when doing I/O.
|
||
|
||
Past efforts to create a "free-threaded" interpreter (one which locks
|
||
shared data at a much finer granularity) have not been successful
|
||
because performance suffered in the common single-processor case. It
|
||
is believed that overcoming this performance issue would make the
|
||
implementation much more complicated and therefore costlier to maintain.
|
||
|
||
|
||
hash-based pyc
|
||
A bytecode cache file that uses the hash rather than the last-modified
|
||
time of the corresponding source file to determine its validity. See
|
||
:ref:`pyc-invalidation`.
|
||
|
||
hashable
|
||
An object is *hashable* if it has a hash value which never changes during
|
||
its lifetime (it needs a :meth:`__hash__` method), and can be compared to
|
||
other objects (it needs an :meth:`__eq__` method). Hashable objects which
|
||
compare equal must have the same hash value.
|
||
|
||
Hashability makes an object usable as a dictionary key and a set member,
|
||
because these data structures use the hash value internally.
|
||
|
||
Most of Python's immutable built-in objects are hashable; mutable
|
||
containers (such as lists or dictionaries) are not; immutable
|
||
containers (such as tuples and frozensets) are only hashable if
|
||
their elements are hashable. Objects which are
|
||
instances of user-defined classes are hashable by default. They all
|
||
compare unequal (except with themselves), and their hash value is derived
|
||
from their :func:`id`.
|
||
|
||
IDLE
|
||
An Integrated Development and Learning Environment for Python.
|
||
:ref:`idle` is a basic editor and interpreter environment
|
||
which ships with the standard distribution of Python.
|
||
|
||
immutable
|
||
An object with a fixed value. Immutable objects include numbers, strings and
|
||
tuples. Such an object cannot be altered. A new object has to
|
||
be created if a different value has to be stored. They play an important
|
||
role in places where a constant hash value is needed, for example as a key
|
||
in a dictionary.
|
||
|
||
import path
|
||
A list of locations (or :term:`path entries <path entry>`) that are
|
||
searched by the :term:`path based finder` for modules to import. During
|
||
import, this list of locations usually comes from :data:`sys.path`, but
|
||
for subpackages it may also come from the parent package's ``__path__``
|
||
attribute.
|
||
|
||
importing
|
||
The process by which Python code in one module is made available to
|
||
Python code in another module.
|
||
|
||
importer
|
||
An object that both finds and loads a module; both a
|
||
:term:`finder` and :term:`loader` object.
|
||
|
||
interactive
|
||
Python has an interactive interpreter which means you can enter
|
||
statements and expressions at the interpreter prompt, immediately
|
||
execute them and see their results. Just launch ``python`` with no
|
||
arguments (possibly by selecting it from your computer's main
|
||
menu). It is a very powerful way to test out new ideas or inspect
|
||
modules and packages (remember ``help(x)``).
|
||
|
||
interpreted
|
||
Python is an interpreted language, as opposed to a compiled one,
|
||
though the distinction can be blurry because of the presence of the
|
||
bytecode compiler. This means that source files can be run directly
|
||
without explicitly creating an executable which is then run.
|
||
Interpreted languages typically have a shorter development/debug cycle
|
||
than compiled ones, though their programs generally also run more
|
||
slowly. See also :term:`interactive`.
|
||
|
||
interpreter shutdown
|
||
When asked to shut down, the Python interpreter enters a special phase
|
||
where it gradually releases all allocated resources, such as modules
|
||
and various critical internal structures. It also makes several calls
|
||
to the :term:`garbage collector <garbage collection>`. This can trigger
|
||
the execution of code in user-defined destructors or weakref callbacks.
|
||
Code executed during the shutdown phase can encounter various
|
||
exceptions as the resources it relies on may not function anymore
|
||
(common examples are library modules or the warnings machinery).
|
||
|
||
The main reason for interpreter shutdown is that the ``__main__`` module
|
||
or the script being run has finished executing.
|
||
|
||
iterable
|
||
An object capable of returning its members one at a time. Examples of
|
||
iterables include all sequence types (such as :class:`list`, :class:`str`,
|
||
and :class:`tuple`) and some non-sequence types like :class:`dict`,
|
||
:term:`file objects <file object>`, and objects of any classes you define
|
||
with an :meth:`__iter__` method or with a :meth:`__getitem__` method
|
||
that implements :term:`sequence` semantics.
|
||
|
||
Iterables can be
|
||
used in a :keyword:`for` loop and in many other places where a sequence is
|
||
needed (:func:`zip`, :func:`map`, ...). When an iterable object is passed
|
||
as an argument to the built-in function :func:`iter`, it returns an
|
||
iterator for the object. This iterator is good for one pass over the set
|
||
of values. When using iterables, it is usually not necessary to call
|
||
:func:`iter` or deal with iterator objects yourself. The ``for``
|
||
statement does that automatically for you, creating a temporary unnamed
|
||
variable to hold the iterator for the duration of the loop. See also
|
||
:term:`iterator`, :term:`sequence`, and :term:`generator`.
|
||
|
||
iterator
|
||
An object representing a stream of data. Repeated calls to the iterator's
|
||
:meth:`~iterator.__next__` method (or passing it to the built-in function
|
||
:func:`next`) return successive items in the stream. When no more data
|
||
are available a :exc:`StopIteration` exception is raised instead. At this
|
||
point, the iterator object is exhausted and any further calls to its
|
||
:meth:`__next__` method just raise :exc:`StopIteration` again. Iterators
|
||
are required to have an :meth:`__iter__` method that returns the iterator
|
||
object itself so every iterator is also iterable and may be used in most
|
||
places where other iterables are accepted. One notable exception is code
|
||
which attempts multiple iteration passes. A container object (such as a
|
||
:class:`list`) produces a fresh new iterator each time you pass it to the
|
||
:func:`iter` function or use it in a :keyword:`for` loop. Attempting this
|
||
with an iterator will just return the same exhausted iterator object used
|
||
in the previous iteration pass, making it appear like an empty container.
|
||
|
||
More information can be found in :ref:`typeiter`.
|
||
|
||
.. impl-detail::
|
||
|
||
CPython does not consistently apply the requirement that an iterator
|
||
define :meth:`__iter__`.
|
||
|
||
key function
|
||
A key function or collation function is a callable that returns a value
|
||
used for sorting or ordering. For example, :func:`locale.strxfrm` is
|
||
used to produce a sort key that is aware of locale specific sort
|
||
conventions.
|
||
|
||
A number of tools in Python accept key functions to control how elements
|
||
are ordered or grouped. They include :func:`min`, :func:`max`,
|
||
:func:`sorted`, :meth:`list.sort`, :func:`heapq.merge`,
|
||
:func:`heapq.nsmallest`, :func:`heapq.nlargest`, and
|
||
:func:`itertools.groupby`.
|
||
|
||
There are several ways to create a key function. For example. the
|
||
:meth:`str.lower` method can serve as a key function for case insensitive
|
||
sorts. Alternatively, a key function can be built from a
|
||
:keyword:`lambda` expression such as ``lambda r: (r[0], r[2])``. Also,
|
||
:func:`operator.attrgetter`, :func:`operator.itemgetter`, and
|
||
:func:`operator.methodcaller` are three key function constructors. See the :ref:`Sorting HOW TO
|
||
<sortinghowto>` for examples of how to create and use key functions.
|
||
|
||
keyword argument
|
||
See :term:`argument`.
|
||
|
||
lambda
|
||
An anonymous inline function consisting of a single :term:`expression`
|
||
which is evaluated when the function is called. The syntax to create
|
||
a lambda function is ``lambda [parameters]: expression``
|
||
|
||
LBYL
|
||
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.
|
||
|
||
locale encoding
|
||
On Unix, it is the encoding of the LC_CTYPE locale. It can be set with
|
||
:func:`locale.setlocale(locale.LC_CTYPE, new_locale) <locale.setlocale>`.
|
||
|
||
On Windows, it is the ANSI code page (ex: ``"cp1252"``).
|
||
|
||
On Android and VxWorks, Python uses ``"utf-8"`` as the locale encoding.
|
||
|
||
``locale.getencoding()`` can be used to get the locale encoding.
|
||
|
||
See also the :term:`filesystem encoding and error handler`.
|
||
|
||
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 is 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`.
|
||
|
||
magic method
|
||
.. index:: pair: magic; method
|
||
|
||
An informal synonym for :term:`special method`.
|
||
|
||
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 :term:`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>`.
|
||
|
||
See :class:`importlib.abc.MetaPathFinder` for the methods that meta path
|
||
finders implement.
|
||
|
||
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
|
||
<https://www.python.org/download/releases/2.3/mro/>`_ for details of the
|
||
algorithm used by the Python interpreter since the 2.3 release.
|
||
|
||
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`.
|
||
|
||
module spec
|
||
A namespace containing the import-related information used to load a
|
||
module. An instance of :class:`importlib.machinery.ModuleSpec`.
|
||
|
||
MRO
|
||
See :term:`method resolution order`.
|
||
|
||
mutable
|
||
Mutable objects can change their value but keep their :func:`id`. See
|
||
also :term:`immutable`.
|
||
|
||
named tuple
|
||
The term "named tuple" applies to any type or class that inherits from
|
||
tuple and whose indexable elements are also accessible using named
|
||
attributes. The type or class may have other features as well.
|
||
|
||
Several built-in types are named tuples, including the values returned
|
||
by :func:`time.localtime` and :func:`os.stat`. Another example is
|
||
:data:`sys.float_info`::
|
||
|
||
>>> sys.float_info[1] # indexed access
|
||
1024
|
||
>>> sys.float_info.max_exp # named field access
|
||
1024
|
||
>>> isinstance(sys.float_info, tuple) # kind of tuple
|
||
True
|
||
|
||
Some named tuples are built-in types (such as the above examples).
|
||
Alternatively, a named tuple can be created from a regular class
|
||
definition that inherits from :class:`tuple` and that defines named
|
||
fields. Such a class can be written by hand or it can be created with
|
||
the factory function :func:`collections.namedtuple`. The latter
|
||
technique also adds some extra methods that may not be found in
|
||
hand-written or built-in named tuples.
|
||
|
||
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 a
|
||
``__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): ...
|
||
|
||
.. _positional-only_parameter:
|
||
|
||
* :dfn:`positional-only`: specifies an argument that can be supplied only
|
||
by position. Positional-only parameters can be defined by including a
|
||
``/`` character in the parameter list of the function definition after
|
||
them, for example *posonly1* and *posonly2* in the following::
|
||
|
||
def func(posonly1, posonly2, /, positional_or_keyword): ...
|
||
|
||
.. _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`.
|
||
|
||
See :class:`importlib.abc.PathEntryFinder` for the methods that path entry
|
||
finders implement.
|
||
|
||
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.
|
||
|
||
path-like object
|
||
An object representing a file system path. A path-like object is either
|
||
a :class:`str` or :class:`bytes` object representing a path, or an object
|
||
implementing the :class:`os.PathLike` protocol. An object that supports
|
||
the :class:`os.PathLike` protocol can be converted to a :class:`str` or
|
||
:class:`bytes` file system path by calling the :func:`os.fspath` function;
|
||
:func:`os.fsdecode` and :func:`os.fsencode` can be used to guarantee a
|
||
:class:`str` or :class:`bytes` result instead, respectively. Introduced
|
||
by :pep:`519`.
|
||
|
||
PEP
|
||
Python Enhancement Proposal. A PEP is a design document
|
||
providing information to the Python community, or describing a new
|
||
feature for Python or its processes or environment. PEPs should
|
||
provide a concise technical specification and a rationale for proposed
|
||
features.
|
||
|
||
PEPs are intended to be the primary mechanisms for proposing major new
|
||
features, for collecting community input on an issue, and for documenting
|
||
the design decisions that have gone into Python. The PEP author is
|
||
responsible for building consensus within the community and documenting
|
||
dissenting opinions.
|
||
|
||
See :pep:`1`.
|
||
|
||
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 API
|
||
A provisional API is one which has been deliberately excluded from
|
||
the standard library's backwards compatibility guarantees. While major
|
||
changes to such interfaces are not expected, as long as they are marked
|
||
provisional, backwards incompatible changes (up to and including removal
|
||
of the interface) may occur if deemed necessary by core developers. Such
|
||
changes will not be made gratuitously -- they will occur only if serious
|
||
fundamental flaws are uncovered that were missed prior to the inclusion
|
||
of the API.
|
||
|
||
Even for provisional APIs, backwards incompatible changes are seen as
|
||
a "solution of last resort" - every attempt will still be made to find
|
||
a backwards compatible resolution to any identified problems.
|
||
|
||
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.
|
||
|
||
provisional package
|
||
See :term:`provisional API`.
|
||
|
||
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. Some objects are
|
||
"immortal" and have reference counts that are never modified, and
|
||
therefore the objects are never deallocated. Reference counting is
|
||
generally not visible to Python code, but it is a key element of the
|
||
:term:`CPython` implementation. Programmers can call the
|
||
:func:`sys.getrefcount` function 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.ABCMeta.register`.
|
||
|
||
set comprehension
|
||
A compact way to process all or part of the elements in an iterable and
|
||
return a set with the results. ``results = {c for c in 'abracadabra' if
|
||
c not in 'abc'}`` generates the set of strings ``{'r', 'd'}``. See
|
||
:ref:`comprehensions`.
|
||
|
||
single dispatch
|
||
A form of :term:`generic function` dispatch where the implementation is
|
||
chosen based on the type of a single argument.
|
||
|
||
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.
|
||
|
||
soft deprecated
|
||
A soft deprecation can be used when using an API which should no longer
|
||
be used to write new code, but it remains safe to continue using it in
|
||
existing code. The API remains documented and tested, but will not be
|
||
developed further (no enhancement).
|
||
|
||
The main difference between a "soft" and a (regular) "hard" deprecation
|
||
is that the soft deprecation does not imply scheduling the removal of the
|
||
deprecated API.
|
||
|
||
Another difference is that a soft deprecation does not issue a warning.
|
||
|
||
See `PEP 387: Soft Deprecation
|
||
<https://peps.python.org/pep-0387/#soft-deprecation>`_.
|
||
|
||
special method
|
||
.. index:: pair: 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`.
|
||
|
||
strong reference
|
||
In Python's C API, a strong reference is a reference to an object
|
||
which is owned by the code holding the reference. The strong
|
||
reference is taken by calling :c:func:`Py_INCREF` when the
|
||
reference is created and released with :c:func:`Py_DECREF`
|
||
when the reference is deleted.
|
||
|
||
The :c:func:`Py_NewRef` function can be used to create a strong reference
|
||
to an object. Usually, the :c:func:`Py_DECREF` function must be called on
|
||
the strong reference before exiting the scope of the strong reference, to
|
||
avoid leaking one reference.
|
||
|
||
See also :term:`borrowed reference`.
|
||
|
||
text encoding
|
||
A string in Python is a sequence of Unicode code points (in range
|
||
``U+0000``--``U+10FFFF``). To store or transfer a string, it needs to be
|
||
serialized as a sequence of bytes.
|
||
|
||
Serializing a string into a sequence of bytes is known as "encoding", and
|
||
recreating the string from the sequence of bytes is known as "decoding".
|
||
|
||
There are a variety of different text serialization
|
||
:ref:`codecs <standard-encodings>`, which are collectively referred to as
|
||
"text encodings".
|
||
|
||
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 :term:`text encoding` automatically.
|
||
Examples of text files are files opened in text mode (``'r'`` or ``'w'``),
|
||
:data:`sys.stdin`, :data:`sys.stdout`, and instances of
|
||
:class:`io.StringIO`.
|
||
|
||
See also :term:`binary file` for a file object able to read and write
|
||
:term:`bytes-like objects <bytes-like object>`.
|
||
|
||
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)``.
|
||
|
||
type alias
|
||
A synonym for a type, created by assigning the type to an identifier.
|
||
|
||
Type aliases are useful for simplifying :term:`type hints <type hint>`.
|
||
For example::
|
||
|
||
def remove_gray_shades(
|
||
colors: list[tuple[int, int, int]]) -> list[tuple[int, int, int]]:
|
||
pass
|
||
|
||
could be made more readable like this::
|
||
|
||
Color = tuple[int, int, int]
|
||
|
||
def remove_gray_shades(colors: list[Color]) -> list[Color]:
|
||
pass
|
||
|
||
See :mod:`typing` and :pep:`484`, which describe this functionality.
|
||
|
||
type hint
|
||
An :term:`annotation` that specifies the expected type for a variable, a class
|
||
attribute, or a function parameter or return value.
|
||
|
||
Type hints are optional and are not enforced by Python but
|
||
they are useful to static type analysis tools, and aid IDEs with code
|
||
completion and refactoring.
|
||
|
||
Type hints of global variables, class attributes, and functions,
|
||
but not local variables, can be accessed using
|
||
:func:`typing.get_type_hints`.
|
||
|
||
See :mod:`typing` and :pep:`484`, which describe this functionality.
|
||
|
||
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:`bytes.splitlines` for an additional use.
|
||
|
||
variable annotation
|
||
An :term:`annotation` of a variable or a class attribute.
|
||
|
||
When annotating a variable or a class attribute, assignment is optional::
|
||
|
||
class C:
|
||
field: 'annotation'
|
||
|
||
Variable annotations are usually used for
|
||
:term:`type hints <type hint>`: for example this variable is expected to take
|
||
:class:`int` values::
|
||
|
||
count: int = 0
|
||
|
||
Variable annotation syntax is explained in section :ref:`annassign`.
|
||
|
||
See :term:`function annotation`, :pep:`484`
|
||
and :pep:`526`, which describe this functionality.
|
||
Also see :ref:`annotations-howto`
|
||
for best practices on working with annotations.
|
||
|
||
virtual environment
|
||
A cooperatively isolated runtime environment that allows Python users
|
||
and applications to install and upgrade Python distribution packages
|
||
without interfering with the behaviour of other Python applications
|
||
running on the same system.
|
||
|
||
See also :mod:`venv`.
|
||
|
||
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.
|