:ref:`2to3-reference`.
abstract base class
- :ref:`abstract-base-classes` complement :term:`duck-typing` by
+ Abstract base classes complement :term:`duck-typing` by
providing a way to define interfaces when other techniques like
- :func:`hasattr` would be clumsy. Python comes with many built-in ABCs for
+ :func:`hasattr` would be clumsy or subtly wrong (for example with
+ :ref:`magic methods <special-lookup>`). Python comes with many built-in ABCs for
data structures (in the :mod:`collections` module), numbers (in the
- :mod:`numbers` module), and streams (in the :mod:`io` module). You can
- create your own ABC with the :mod:`abc` module.
+ :mod:`numbers` module), streams (in the :mod:`io` module), import finders
+ and loaders (in the :mod:`importlib.abc` module). You can create your own
+ ABCs with the :mod:`abc` module.
argument
A value passed to a function or method, assigned to a named local
mapping
A container object that supports arbitrary key lookups and implements the
methods specified in the :class:`Mapping` or :class:`MutableMapping`
- :ref:`abstract base classes <abstract-base-classes>`. Examples include
- :class:`dict`, :class:`collections.defaultdict`,
+ :ref:`abstract base classes <collections-abstract-base-classes>`. Examples
+ include :class:`dict`, :class:`collections.defaultdict`,
:class:`collections.OrderedDict` and :class:`collections.Counter`.
metaclass
--------------
This module provides the infrastructure for defining an :term:`abstract base
-class` (ABCs) in Python, as outlined in :pep:`3119`; see the PEP for why this
+class` (ABC) in Python, as outlined in :pep:`3119`; see the PEP for why this
was added to Python. (See also :pep:`3141` and the :mod:`numbers` module
regarding a type hierarchy for numbers based on ABCs.)
===================== ====================================================================
In addition to the concrete container classes, the collections module provides
-:ref:`abstract-base-classes` that can be used to test whether a class provides a
-particular interface, for example, whether it is hashable or a mapping.
+:ref:`abstract base classes <collections-abstract-base-classes>` that can be
+used to test whether a class provides a particular interface, for example,
+whether it is hashable or a mapping.
:class:`Counter` objects
subclass) or an arbitrary sequence which can be converted into a string using
the built-in :func:`str` function.
-.. _abstract-base-classes:
+.. _collections-abstract-base-classes:
ABCs - abstract base classes
----------------------------
:synopsis: Numeric abstract base classes (Complex, Real, Integral, etc.).
-The :mod:`numbers` module (:pep:`3141`) defines a hierarchy of numeric abstract
-base classes which progressively define more operations. None of the types
-defined in this module can be instantiated.
+The :mod:`numbers` module (:pep:`3141`) defines a hierarchy of numeric
+:term:`abstract base classes <abstract base class>` which progressively define
+more operations. None of the types defined in this module can be instantiated.
.. class:: Number