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diff --git a/Doc/howto/functional.rst b/Doc/howto/functional.rst index bfd2c96..175eeae 100644 --- a/Doc/howto/functional.rst +++ b/Doc/howto/functional.rst @@ -1010,135 +1010,6 @@ Some of the functions in this module are: Consult the operator module's documentation for a complete list. - -The functional module ---------------------- - -Collin Winter's `functional module <http://oakwinter.com/code/functional/>`__ -provides a number of more advanced tools for functional programming. It also -reimplements several Python built-ins, trying to make them more intuitive to -those used to functional programming in other languages. - -This section contains an introduction to some of the most important functions in -``functional``; full documentation can be found at `the project's website -<http://oakwinter.com/code/functional/documentation/>`__. - -``compose(outer, inner, unpack=False)`` - -The ``compose()`` function implements function composition. In other words, it -returns a wrapper around the ``outer`` and ``inner`` callables, such that the -return value from ``inner`` is fed directly to ``outer``. That is, :: - - >>> def add(a, b): - ... return a + b - ... - >>> def double(a): - ... return 2 * a - ... - >>> compose(double, add)(5, 6) - 22 - -is equivalent to :: - - >>> double(add(5, 6)) - 22 - -The ``unpack`` keyword is provided to work around the fact that Python functions -are not always `fully curried <http://en.wikipedia.org/wiki/Currying>`__. By -default, it is expected that the ``inner`` function will return a single object -and that the ``outer`` function will take a single argument. Setting the -``unpack`` argument causes ``compose`` to expect a tuple from ``inner`` which -will be expanded before being passed to ``outer``. Put simply, :: - - compose(f, g)(5, 6) - -is equivalent to:: - - f(g(5, 6)) - -while :: - - compose(f, g, unpack=True)(5, 6) - -is equivalent to:: - - f(*g(5, 6)) - -Even though ``compose()`` only accepts two functions, it's trivial to build up a -version that will compose any number of functions. We'll use -:func:`functools.reduce`, ``compose()`` and ``partial()`` (the last of which is -provided by both ``functional`` and ``functools``). :: - - from functional import compose, partial - import functools - - - multi_compose = partial(functools.reduce, compose) - - -We can also use ``map()``, ``compose()`` and ``partial()`` to craft a version of -``"".join(...)`` that converts its arguments to string:: - - from functional import compose, partial - - join = compose("".join, partial(map, str)) - - -``flip(func)`` - -``flip()`` wraps the callable in ``func`` and causes it to receive its -non-keyword arguments in reverse order. :: - - >>> def triple(a, b, c): - ... return (a, b, c) - ... - >>> triple(5, 6, 7) - (5, 6, 7) - >>> - >>> flipped_triple = flip(triple) - >>> flipped_triple(5, 6, 7) - (7, 6, 5) - -``foldl(func, start, iterable)`` - -``foldl()`` takes a binary function, a starting value (usually some kind of -'zero'), and an iterable. The function is applied to the starting value and the -first element of the list, then the result of that and the second element of the -list, then the result of that and the third element of the list, and so on. - -This means that a call such as:: - - foldl(f, 0, [1, 2, 3]) - -is equivalent to:: - - f(f(f(0, 1), 2), 3) - - -``foldl()`` is roughly equivalent to the following recursive function:: - - def foldl(func, start, seq): - if len(seq) == 0: - return start - - return foldl(func, func(start, seq[0]), seq[1:]) - -Speaking of equivalence, the above ``foldl`` call can be expressed in terms of -the built-in :func:`functools.reduce` like so:: - - import functools - functools.reduce(f, [1, 2, 3], 0) - - -We can use ``foldl()``, ``operator.concat()`` and ``partial()`` to write a -cleaner, more aesthetically-pleasing version of Python's ``"".join(...)`` -idiom:: - - from functional import foldl, partial from operator import concat - - join = partial(foldl, concat, "") - - Small functions and the lambda expression ========================================= |