Issue #4331: Added functools.partialmethod

Initial patch by Alon Horev

2 files changed, 61 insertions, 2 deletions

diff --git a/Doc/library/functools.rst b/Doc/library/functools.rst
index 14e1351..4eb263a 100644
--- a/Doc/library/functools.rst
+++ b/Doc/library/functools.rst
@@ -194,6 +194,48 @@ The :mod:`functools` module defines the following functions:
       18
 
 
+.. class:: partialmethod(func, *args, **keywords)
+
+   Return a new :class:`partialmethod` descriptor which behaves
+   like :class:`partial` except that it is designed to be used as a method
+   definition rather than being directly callable.
+
+   *func* must be a :term:`descriptor` or a callable (objects which are both,
+   like normal functions, are handled as descriptors).
+
+   When *func* is a descriptor (such as a normal Python function,
+   :func:`classmethod`, :func:`staticmethod`, :func:`abstractmethod` or
+   another instance of :class:`partialmethod`), calls to ``__get__`` are
+   delegated to the underlying descriptor, and an appropriate
+   :class:`partial` object returned as the result.
+
+   When *func* is a non-descriptor callable, an appropriate bound method is
+   created dynamically. This behaves like a normal Python function when
+   used as a method: the *self* argument will be inserted as the first
+   positional argument, even before the *args* and *keywords* supplied to
+   the :class:`partialmethod` constructor.
+
+   Example::
+
+      >>> class Cell(object):
+      ...     @property
+      ...     def alive(self):
+      ...         return self._alive
+      ...     def set_state(self, state):
+      ...         self._alive = bool(state)
+      ...     set_alive = partialmethod(set_alive, True)
+      ...     set_dead = partialmethod(set_alive, False)
+      ...
+      >>> c = Cell()
+      >>> c.alive
+      False
+      >>> c.set_alive()
+      >>> c.alive
+      True
+
+   .. versionadded:: 3.4
+
+
 .. function:: reduce(function, iterable[, initializer])
 
    Apply *function* of two arguments cumulatively to the items of *sequence*, from
@@ -431,4 +473,3 @@ differences.  For instance, the :attr:`__name__` and :attr:`__doc__` attributes
 are not created automatically.  Also, :class:`partial` objects defined in
 classes behave like static methods and do not transform into bound methods
 during instance attribute look-up.
-
diff --git a/Doc/whatsnew/3.4.rst b/Doc/whatsnew/3.4.rst
index a570af8..ed6daee 100644
--- a/Doc/whatsnew/3.4.rst
+++ b/Doc/whatsnew/3.4.rst
@@ -342,7 +342,25 @@ handling).
 functools
 ---------
 
-New :func:`functools.singledispatch` decorator: see the :pep:`443`.
+The new :func:`~functools.partialmethod` descriptor bring partial argument
+application to descriptors, just as :func:`~functools.partial` provides
+for normal callables. The new descriptor also makes it easier to get
+arbitrary callables (including :func:`~functools.partial` instances)
+to behave like normal instance methods when included in a class definition.
+
+(Contributed by Alon Horev and Nick Coghlan in :issue:`4331`)
+
+The new :func:`~functools.singledispatch` decorator brings support for
+single-dispatch generic functions to the Python standard library. Where
+object oriented programming focuses on grouping multiple operations on a
+common set of data into a class, a generic function focuses on grouping
+multiple implementations of an operation that allows it to work with
+*different* kinds of data.
+
+.. seealso::
+
+   :pep:`443` - Single-dispatch generic functions
+      PEP written and implemented by Łukasz Langa.
 
 
 hashlib