Chapter 53 - HigherOrderFunctions.py

# CHAPTER 53
# Higher Order Functions
# A function that either:
#   1. Accepts a function as argument
#   2. Returns a function
#   (In Python, functions are also treated as objects)


# Part 1 Demonstration
# Functions that accepts a function as argument

def loud(text):
    return text.upper()

def quiet(text):
    return text.lower()

# This is the higher order functions
def hello(func):
    text = func("Hello")
    print(text)

# prints "HELLO"
# loud function is pass to hello function
# then inside the hello function:
#       text = loud("Hello")
# now, print the text
hello(loud)

# prints "hello"
# loud function is pass to hello function
# then inside the hello function:
#       text = quiet("Hello")
# now, print the text
hello(quiet)



# Part 2 Demonstration
# Functions returns a function

def divisor(x):
    def dividend(y):
        return y / x
    return dividend

divide = divisor(2)
# How this prints to 5.0?
# First, the divisor(2)
# returns the memory address of divisor and
# x already equals to 2, then it returns the dividend
# waiting for y

# Now, after another call
# The y is equal to 10
# So, the dividend function inside function will be called
# Returning 5.0 and it will be printed
print(divide(10))