/documentation_files/__future__.py
Python | 88 lines | 61 code | 16 blank | 11 comment | 7 complexity | e51c917620dbc0f54643417686f2a9c9 MD5 | raw file
- #!/usr/bin/env python2.7
- # -*- coding: utf-8 -*-
- """:synopsis: Future statement definitions
- :mod:`__future__` is a real module, and serves three purposes:
- * To avoid confusing existing tools that analyze import statements and expect to
- find the modules they're importing.
- * To ensure that :ref:`future statements <future>` run under releases prior to
- 2.1 at least yield runtime exceptions (the import of :mod:`__future__` will
- fail, because there was no module of that name prior to 2.1).
- * To document when incompatible changes were introduced, and when they will be
- --- or were --- made mandatory. This is a form of executable documentation, and
- can be inspected programmatically via importing :mod:`__future__` and examining
- its contents.
- Each statement in :file:`__future__.py` is of the form::
- FeatureName = _Feature(OptionalRelease, MandatoryRelease,
- CompilerFlag)
- where, normally, *OptionalRelease* is less than *MandatoryRelease*, and both are
- 5-tuples of the same form as ``sys.version_info``::
- (PY_MAJOR_VERSION, # the 2 in 2.1.0a3; an int
- PY_MINOR_VERSION, # the 1; an int
- PY_MICRO_VERSION, # the 0; an int
- PY_RELEASE_LEVEL, # "alpha", "beta", "candidate" or "final"; string
- PY_RELEASE_SERIAL # the 3; an int
- )
- *OptionalRelease* records the first release in which the feature was accepted.
- In the case of a *MandatoryRelease* that has not yet occurred,
- *MandatoryRelease* predicts the release in which the feature will become part of
- the language.
- Else *MandatoryRelease* records when the feature became part of the language; in
- releases at or after that, modules no longer need a future statement to use the
- feature in question, but may continue to use such imports.
- *MandatoryRelease* may also be ``None``, meaning that a planned feature got
- dropped.
- Instances of class :class:`_Feature` have two corresponding methods,
- :meth:`getOptionalRelease` and :meth:`getMandatoryRelease`.
- *CompilerFlag* is the (bitfield) flag that should be passed in the fourth
- argument to the built-in function :func:`compile` to enable the feature in
- dynamically compiled code. This flag is stored in the :attr:`compiler_flag`
- attribute on :class:`_Feature` instances.
- No feature description will ever be deleted from :mod:`__future__`. Since its
- introduction in Python 2.1 the following features have found their way into the
- language using this mechanism:
- +------------------+-------------+--------------+---------------------------------------------+
- | feature | optional in | mandatory in | effect |
- +==================+=============+==============+=============================================+
- | nested_scopes | 2.1.0b1 | 2.2 | :pep:`227`: |
- | | | | *Statically Nested Scopes* |
- +------------------+-------------+--------------+---------------------------------------------+
- | generators | 2.2.0a1 | 2.3 | :pep:`255`: |
- | | | | *Simple Generators* |
- +------------------+-------------+--------------+---------------------------------------------+
- | division | 2.2.0a2 | 3.0 | :pep:`238`: |
- | | | | *Changing the Division Operator* |
- +------------------+-------------+--------------+---------------------------------------------+
- | absolute_import | 2.5.0a1 | 2.7 | :pep:`328`: |
- | | | | *Imports: Multi-Line and Absolute/Relative* |
- +------------------+-------------+--------------+---------------------------------------------+
- | with_statement | 2.5.0a1 | 2.6 | :pep:`343`: |
- | | | | *The "with" Statement* |
- +------------------+-------------+--------------+---------------------------------------------+
- | print_function | 2.6.0a2 | 3.0 | :pep:`3105`: |
- | | | | *Make print a function* |
- +------------------+-------------+--------------+---------------------------------------------+
- | unicode_literals | 2.6.0a2 | 3.0 | :pep:`3112`: |
- | | | | *Bytes literals in Python 3000* |
- +------------------+-------------+--------------+---------------------------------------------+
- """
- def print_function(): pass