Expand Up @@ -39,6 +39,20 @@ Glossary and loaders (in the :mod:`importlib.abc` module). You can create your own ABCs with the :mod:`abc` module.
annotation A label associated with a variable, a class attribute or a function parameter or return value, used by convention as a :term:`type hint`.
Annotations of local variables cannot be accessed at runtime, but annotations of global variables, class attributes, and functions are stored in the :attr:`__annotations__` special attribute of modules, classes, and functions, respectively.
See :term:`variable annotation`, :term:`function annotation`, :pep:`484` and :pep:`526`, which describe this functionality.
argument A value passed to a :term:`function` (or :term:`method`) when calling the function. There are two kinds of argument: Expand Down Expand Up @@ -175,6 +189,10 @@ Glossary normally contain method definitions which operate on instances of the class.
class variable A variable defined in a class and intended to be modified only at class level (i.e., not in an instance of the class).
coercion The implicit conversion of an instance of one type to another during an operation which involves two arguments of the same type. For example, Expand Down Expand Up @@ -367,14 +385,20 @@ Glossary and the :ref:`function` section.
function annotation An arbitrary metadata value associated with a function parameter or return value. Its syntax is explained in section :ref:`function`. Annotations may be accessed via the :attr:`__annotations__` special attribute of a function object. 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` return value::
def sum_two_numbers(a: int, b: int) -> int: return a + b
Function annotation syntax is explained in section :ref:`function`.
Python itself does not assign any particular meaning to function annotations. They are intended to be interpreted by third-party libraries or tools. See :pep:`3107`, which describes some of their potential uses. See :term:`variable annotation` and :pep:`484`, which describe this functionality.
__future__ A pseudo-module which programmers can use to enable new language features Expand Down Expand Up @@ -1016,6 +1040,43 @@ Glossary :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::
from typing import List, Tuple
def remove_gray_shades( colors: List[Tuple[int, int, int]]) -> List[Tuple[int, int, int]]: pass
could be made more readable like this::
from typing import List, Tuple
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'``, Expand All @@ -1024,16 +1085,23 @@ Glossary :func:`bytes.splitlines` for an additional use.
variable annotation A type metadata value associated with a module global variable or a class attribute. Its syntax is explained in section :ref:`annassign`. Annotations are stored in the :attr:`__annotations__` special attribute of a class or module object and can be accessed using :func:`typing.get_type_hints`. 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`.
Python itself does not assign any particular meaning to variable annotations. They are intended to be interpreted by third-party libraries or type checking tools. See :pep:`526`, :pep:`484` which describe some of their potential uses. See :term:`function annotation`, :pep:`484` and :pep:`526`, which describe this functionality.
virtual environment A cooperatively isolated runtime environment that allows Python users Expand Down