Simple example of a higher order function

higher_order.py

#!/usr/bin/env python3

# A classic example:

# create_increaser_by(num) returns a new function, the returned function adds num to it's arg
def create_increaser_by(num):
    # This function is weirdly named because it's returned later on.
    # It's not the name it will be called by
    def _return_fun(arg):
        return arg + num

    # As you see, _return_fun was declared as a function and is return
    # just like anything else
    return _return_fun

# So let's try creating a function that adds 1 to anything
one_adder = create_increaser_by(1)

# one_adder is now a function that adds 1 to it's arg
print(one_adder(1)) # => 2
print(one_adder(2)) # => 3

print(one_adder(one_adder(1))) # => 3