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diff --git a/Doc/library/functools.rst b/Doc/library/functools.rst index 94be636..1511a25 100644 --- a/Doc/library/functools.rst +++ b/Doc/library/functools.rst @@ -15,6 +15,51 @@ function for the purposes of this module. The :mod:`functools` module defines the following functions: +.. function:: cmp_to_key(func) + + Transform an old-style comparison function to a key-function. Used with + tools that accept key functions (such as :func:`sorted`, :func:`min`, + :func:`max`, :func:`heapq.nlargest`, :func:`heapq.nsmallest`, + :func:`itertools.groupby`). + This function is primarily used as a transition tool for programs + being converted from Py2.x which supported the use of comparison + functions. + + A compare function is any callable that accept two arguments, compares + them, and returns a negative number for less-than, zero for equality, + or a positive number for greater-than. A key function is a callable + that accepts one argument and returns another value that indicates + the position in the desired collation sequence. + + Example:: + + sorted(iterable, key=cmp_to_key(locale.strcoll)) # locale-aware sort order + + .. versionadded:: 3.2 + +.. function:: total_ordering(cls) + + Given a class defining one or more rich comparison ordering methods, this + class decorator supplies the rest. This simplies the effort involved + in specifying all of the possible rich comparison operations: + + The class must define one of :meth:`__lt__`, :meth:`__le__`, + :meth:`__gt__`, or :meth:`__ge__`. + In addition, the class should supply an :meth:`__eq__` method. + + For example:: + + @total_ordering + class Student: + def __eq__(self, other): + return ((self.lastname.lower(), self.firstname.lower()) == + (other.lastname.lower(), other.firstname.lower())) + def __lt__(self, other): + return ((self.lastname.lower(), self.firstname.lower()) < + (other.lastname.lower(), other.firstname.lower())) + + .. versionadded:: 3.2 + .. function:: partial(func, *args, **keywords) Return a new :class:`partial` object which when called will behave like *func* |