Function composition in python

compose.py

from functools import partial

def _composed(f, g, *args, **kwargs):
    return f(g(*args, **kwargs))

def compose(*a):
    try:
        return partial(_composed, a[0], compose(*a[1:]))
    except:
        return a[0]

There is a very old, but still relevant (despite the additions to stdlib in later times, like partial) functional.py module (I can't find it's homepage, maybe it expired, its still in cheeseshop though) which I use. It's compose function looks like this:

def compose(func_1, func_2):
    """
    compose(func_1, func_2) -> function

    The function returned by compose is a composition of func_1 and func_2.
    That is, compose(func_1, func_2)(5) == func_1(func_2(5))
    """
    if not callable(func_1):
        raise TypeError("First argument to compose must be callable")
    if not callable(func_2):
        raise TypeError("Second argument to compose must be callable")

    def composition(*args, **kwargs):
        return func_1(func_2(*args, **kwargs))
    return composition

One can define multicompose in terms of fold and compose:

multicompose = lambda *funs: reduce(compose, funs)

Relevant: https://mathieularose.com/function-composition-in-python/

A comment from Fred Loney, gives an elegant solution:

def compose(*funcs):
    return lambda x: reduce(lambda v, f: f(v), reversed(funcs), x)