Compose functions functionally.

compose.py

from functools import reduce


def compose(*functions, forward=False):
    """Compose many (single-argument) functions into a single function

    Evalutates the fuctions last-to-first by default.  Use functools.partial
    with this for multiargument functions.

    Also, it is magic.  Don't play with it or you'll let the magic out.

    "Some things you just... maybe shouldn't be allowed to do in a programming
    language.  The human brain is too stupid to utilize computers properly, it
    seems."

    Args:
        *functions (function, function, ...): an arbitrary number of functions
        forward (boolean): evaluate the functions first-to-last

    Returns:
        The composition of *functions, i.e.
        compose(f, g, h)(x) = f(g(h(x)))

    Examples:
        >>> f, g = lambda x: x*2, lambda x: x+2
        >>> assert f(g(2)))) == compose(f, g)(2)
        >>> assert g(f(2)))) == compose(f, g, forward=True)(2)
    """
    if forward:
        return lambda x: reduce(lambda v, f: f(v), functions, x)
    else:
        return lambda x: reduce(lambda v, f: f(v), reversed(functions), x)