In Python, functions are objects too

# - compatibility with Python 3
from __future__ import print_function  # print('me') instead of print 'me'
from __future__ import division  # 1/2 == 0.5, not 0

If I make a string in Python:

name = 'Matthew'

then I have a Python object of type str:

type(name)

str

Let's say I defined a function add:

def add(a, b):
    return a + b

Now I have another Python object, of type function:

type(add)

function

With my string, I can refer to the same string object, with a different variable name:

prisoner = name
prisoner

'Matthew'

It's the same for functions, because they are objects too:

my_add = add
type(my_add)

function

Functions are objects you can "call" by following the function object name with parentheses and arguments you want to pass:

add(1, 2)

3

my_add(1, 2)

3

As for any other object in Python, you can pass function objects to other functions:

def run_a_func(func, arg1, arg2):
    result = func(arg1, arg2)
    print('Result was', result)

run_a_func(add, 1, 2)

Result was 3

run_a_func(my_add, 1, 2)

Result was 3

def sub(a, b):
    return a - b

run_a_func(sub, 1, 2)

Result was -1