Written by Albert Lam
on January 23, 2021

Improve Your Python Game

Functions are first-class objects in Python

Which means you can do stuff like this:

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def area_of_triangle(length, height):
    return (1/2) * length * height

def area_of_rectangle(length, height):
    return length * height

def volume_of_small_prism(area_of_base, length, height, depth):
    return area_of_base(length, height) * depth

volume_of_small_prism(area_of_triangle, 2, 3, 4)      # returns 12.0
volume_of_small_prism(area_of_rectangle, 2, 3, 5)     # returns 30

Functions can also return other functions

Let’s create a wrapper that returns the correct base area function, depending on which base shape we’ve chosen.

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def area_of_base(shape):
    if shape == "triangle":
        return area_of_triangle
    elif shape == "rectangle":
        return area_of_rectangle
    else:
        print("No function for that shape yet.")

area_of_triangle_check = area_of_base("triangle")
area_of_triangle_check(2, 3)                                # returns 3.0
volume_of_small_prism(area_of_triangle_check, 2, 3, 4)      # returns 12.0

Decorators are syntactic sugar for extending input functions

For example, we can add some text to our function to make it more pretty.

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def prettify_my_function(function):
    def decorator(shape):
        print("Your chosen shape is: %s" %shape)
        return function(shape)
    return decorator

area_of_base = prettify_my_function(area_of_base)
pretty_area_of_triangle = area_of_base("triangle")       
                                    # Your chosen shape is: triangle
pretty_area_of_triangle(2, 3)       # returns 3.0

Python instead allows you to write area_of_base = prettify_my_function(area_of_base) using the @ syntax:

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@prettify_my_function
def area_of_base(shape):
    if shape == "triangle":
        return area_of_triangle
    elif shape == "rectangle":
        return area_of_rectangle
    else:
        print("No function for that shape yet.")

decorated_area_of_triangle = area_of_base("triangle")            
                                        # Your chosen shape is: triangle
decorated_area_of_triangle(2, 3)        # returns 3.0

This is especially useful when you want to reuse your decorator for other functions – imagine if your decorator contained some sizable logic that you wanted to reuse (without something like prettify_my_function, you would have to rewrite a lot of code).

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def perimeter_of_triangle(length, height):
    return length + height + ((length**2 + height**2) ** (1/2))

def perimeter_of_rectangle(length, height):
    return 2 * (length + height)

@prettify_my_function
def perimeter_of_base(shape):
    if shape == "triangle":
        return perimeter_of_triangle
    elif shape == "rectangle":
        return perimeter_of_rectangle
    else:
        print("No function for that shape yet.")

perimeter_of_triangle = perimeter_of_base("triangle")            
                                    # Your chosen shape is: triangle
perimeter_of_triangle(3, 4)         # returns 12.0

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