__future__ — Future statement definitions

Kod źródłowy: Lib/__future__.py

---

__future__ is a real module, and serves three purposes:

• Aby uniknąć pomyłek z istniejącymi narzędziami, które analizują instrukcje importowania i oczekują znalezienia modułów, które importują.

• To ensure that future statements run under releases prior to 2.1 at least yield runtime exceptions (the import of __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 __future__ and examining its contents.

Each statement in __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 _Feature have two corresponding methods, getOptionalRelease() and getMandatoryRelease().

CompilerFlag is the (bitfield) flag that should be passed in the fourth argument to the built-in function compile() to enable the feature in dynamically compiled code. This flag is stored in the compiler_flag attribute on _Feature instances.

No feature description will ever be deleted from __future__. Since its introduction in Python 2.1 the following features have found their way into the language using this mechanism:

cecha	opcjonalne w	obowiązkowe w	effect
nested_scopes	2.1.0b1	2.2	PEP 227: Statically Nested Scopes
generatory	2.2.0a1	2.3	PEP 255: Simple Generators
podział	2.2.0a2	3.0	PEP 238: Zmiana operatora podziału
absolute_import	2.5.0a1	3.0	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
generator_stop	3.5.0b1	3.7	PEP 479: StopIteration handling inside generators
adnotacje typów	3.7.0b1	TBD 1	PEP 563: Postponed evaluation of annotations

1

from __future__ import annotations was previously scheduled to become mandatory in Python 3.10, but the Python Steering Council twice decided to delay the change (announcement for Python 3.10; announcement for Python 3.11). No final decision has been made yet. See also PEP 563 and PEP 649.

Zobacz także

Future statements

Jak kompilator traktuje przyszłe importy.