6.6 functools -- Higher order functions and operations on callable objects.

6.6 functools -- Higher order functions and operations on callable objects.

New in version 2.5.

The functools module is for higher-order functions: functions that act on or return other functions. In general, any callable object can be treated as a function for the purposes of this module.

The functools module defines the following function:

partial( func[,*args][, **keywords])

Return a new partial object which when called will behave like func called with the positional arguments args and keyword arguments keywords. If more arguments are supplied to the call, they are appended to args. If additional keyword arguments are supplied, they extend and override keywords. Roughly equivalent to:

        def partial(func, *args, **keywords):
            def newfunc(*fargs, **fkeywords):
                newkeywords = keywords.copy()
                newkeywords.update(fkeywords)
                return func(*(args + fargs), **newkeywords)
            newfunc.func = func
            newfunc.args = args
            newfunc.keywords = keywords
            return newfunc

The partial is used for partial function application which ``freezes'' some portion of a function's arguments and/or keywords resulting in a new object with a simplified signature. For example, partial can be used to create a callable that behaves like the int function where the base argument defaults to two:

        >>> basetwo = partial(int, base=2)
        >>> basetwo.__doc__ = 'Convert base 2 string to an int.'
        >>> basetwo('10010')
        18

update_wrapper( wrapper, wrapped[, assigned][, updated])

Update a wrapper function to look like the wrapped function. The optional arguments are tuples to specify which attributes of the original function are assigned directly to the matching attributes on the wrapper function and which attributes of the wrapper function are updated with the corresponding attributes from the original function. The default values for these arguments are the module level constants WRAPPER_ASSIGNMENTS (which assigns to the wrapper function's __name__, __module__ and __doc__, the documentation string) and WRAPPER_UPDATES (which updates the wrapper function's __dict__, i.e. the instance dictionary).

The main intended use for this function is in decorator functions which wrap the decorated function and return the wrapper. If the wrapper function is not updated, the metadata of the returned function will reflect the wrapper definition rather than the original function definition, which is typically less than helpful.

wraps( wrapped[, assigned][, updated])

This is a convenience function for invoking partial(update_wrapper, wrapped=wrapped, assigned=assigned, updated=updated) as a function decorator when defining a wrapper function. For example:

        >>> def my_decorator(f):
        ...     @wraps(f)
        ...     def wrapper(*args, **kwds):
        ...         print 'Calling decorated function'
        ...         return f(*args, **kwds)
        ...     return wrapper
        ...
        >>> @my_decorator
        ... def example():
	...     """Docstring"""
        ...     print 'Called example function'
        ...
        >>> example()
        Calling decorated function
        Called example function
        >>> example.__name__
        'example'
	>>> example.__doc__
	'Docstring'

Without the use of this decorator factory, the name of the example function would have been 'wrapper', and the docstring of the original example() would have been lost.

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