Composing functions in python

Question

I have an array of functions and I\'m trying to produce one function which consists of the composition of the elements in my array. My approach is:

def compo         


        

Answer 1

pip install funcoperators is another library to implement it that allows infix notation:

from funcoperators import compose

# display = lambda x: hex(ord(list(x)))
display = hex *compose* ord *compose* list

# also works as a function
display = compose(hex, ord, list)

pip install funcoperators https://pypi.org/project/funcoperators/

Disclaimer: I'm the creator of the module

Answer 2

def compose (*functions):
    def inner(arg):
        for f in reversed(functions):
            arg = f(arg)
        return arg
    return inner

Example:

>>> def square (x):
        return x ** 2
>>> def increment (x):
        return x + 1
>>> def half (x):
        return x / 2

>>> composed = compose(square, increment, half) # square(increment(half(x)))
>>> composed(5) # square(increment(half(5))) = square(increment(2.5)) = square(3.5) = 12,25
12.25

Answer 3

More general solution of Imanol Luengo from my point of view (python notebook example):

from functools import reduce
from functools import partial

def f(*argv, **kwargs):
  print('f: {} {}'.format(argv, kwargs))
  return argv, kwargs

def g(*argv, **kwargs):
  print('g: {} {}'.format(argv, kwargs))
  return argv, kwargs

def compose(fs, *argv, **kwargs):
  return reduce(lambda x, y: y(*x[0], **x[1]), fs, (argv, kwargs))

h = partial(compose, [f, g])
h('value', key='value')
output:
f: ('value',) {'key': 'value'}
g: ('value',) {'key': 'value'}

m = partial(compose, [h, f, g])
m('value', key='value')
output:
f: ('value',) {'key': 'value'}
g: ('value',) {'key': 'value'}
f: ('value',) {'key': 'value'}
g: ('value',) {'key': 'value'}

Answer 4

You can also create an array of functions and use reduce:

def f1(x): return x+1
def f2(x): return x+2
def f3(x): return x+3

x = 5

# Will print f3(f2(f1(x)))
print reduce(lambda acc, x: x(acc), [f1, f2, f3], x)

# As a function:
def compose(*funcs):
    return lambda x: reduce(lambda acc, f: f(acc), funcs, x)

f = compose(f1, f2, f3)

Answer 5

This is my version

def compose(*fargs):
    def inner(arg):
        if not arg:
            raise ValueError("Invalid argument")
        if not all([callable(f) for f in fargs]):
            raise TypeError("Function is not callable")
        return reduce(lambda arg, func: func(arg), fargs, arg)
    return inner

An example of how it's used

def calcMean(iterable):
    return sum(iterable) / len(iterable)


def formatMean(mean):
    return round(float(mean), 2)


def adder(val, value):
    return val + value


def isEven(val):
    return val % 2 == 0

if __name__ == '__main__':
    # Ex1

    rand_range = [random.randint(0, 10000) for x in range(0, 10000)]

    isRandIntEven = compose(calcMean, formatMean,
                            partial(adder, value=0), math.floor.__call__, isEven)

    print(isRandIntEven(rand_range))

Answer 6

The easiest approach would be first to write a composition of 2 functions:

def compose2(f, g):
    return lambda *a, **kw: f(g(*a, **kw))

And then use reduce to compose more functions:

def compose(*fs):
    return reduce(compose2, fs)

Or you can use some library, which already contains compose function.