= Python Functools =

'''`functools`''' is a module supporting the construction of efficient functions.

<<TableOfContents>>

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== Function Composition ==

The module provides `partial` and `partialmethod` functions for function composition.

Try:

{{{
from functools import partial

basetwo = partial(int, base=2)
basetwo('10010')               # 18
}}}

`partialmethod` is used in exactly the same way, and just manages the `self`.

{{{
class Cat:
    def say(self, message):
        print(message)

    meow = partialmethod(say, "Meow!")
}}}

The module also exposes two objects (`functools.Placeholder` and `functools.partial`) which are implementation details of these functions.

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== Function Overloading ==

The module provides `singledispatch` and `singledispatchmethod` decorators for function overloading.

Try:

{{{
from functools import singledispatch

@singledispatch
def makebigger(arg):
    print(arg + 1)

@makebigger.register
def _(arg: string):
    print(arg + "s")

@makebigger.register
def _(list: string):
    print(arg.append(0))
}}}

`singledispatchmethod` is used in exactly the same way, and just dispatches on the second argument (i.e., does not dispatch on the `self`).

----



== Memoization ==

The module provides the `lru_cache` and `cache` decorators for memoization.

{{{
@lru_cache(maxsize=None)
def fib(n):
    if n < 2:
        return n
    return fib(n-1) + fib(n-2)
}}}

Note that `cache` is the same as `lru_cache(maxsize=None)`.

`cached_property` can be made to work in a similar way.

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== Others ==

||'''Function Names'''      ||'''Description'''||
||`functools.cmp_to_key`    || ||
||`functools.reduce`        || ||
||`functools.update_wrapper`|| ||

||'''Decorator Names'''     ||'''Description'''||
||`functools.total_ordering`|| ||
||`functools.wraps`         || ||

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== See also ==

[[https://docs.python.org/3/library/functools.html|Python functools module documentation]]

[[https://pymotw.com/3/functools/|Python Module of the Day article for functools]]



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