First Class functions in Python

First class objects in a language are handled uniformly throughout. They may be stored in data structures, passed as arguments, or used in control structures. A programming language is said to support first-class functions if it treats functions as first-class objects. Python supports the concept of First Class functions.

Properties of first class functions:

• A function is an instance of the Object type.
• You can store the function in a variable.
• You can pass the function as a parameter to another function.
• You can return the function from a function.
• You can store them in data structures such as hash tables, lists, …

Examples illustrating First Class functions in Python

1. Functions are objects: Python functions are first class objects. In the example below, we are assigning function to a variable. This assignment doesn’t call the function. It takes the function object referenced by shout and creates a second name pointing to it, yell.

# Python program to illustrate functions
# can be treated as objects
def shout(text):
    return text.upper()

print (shout('Hello'))

yell = shout

print (yell('Hello'))

Output:

HELLO
HELLO

2. Functions can be passed as arguments to other functions: Because functions are objects we can pass them as arguments to other functions. Functions that can accept other functions as arguments are also called higher-order functions. In the example below, we have created a function greet which takes a function as an argument.

# Python program to illustrate functions
# can be passed as arguments to other functions
def shout(text):
    return text.upper()

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

def greet(func):
    # storing the function in a variable
    greeting = func("""Hi, I am created by a function
                    passed as an argument.""")
    print (greeting)

greet(shout)
greet(whisper)

Output

HI, I AM CREATED BY A FUNCTION PASSED AS AN ARGUMENT.
hi, i am created by a function passed as an argument.

3. Functions can return another function: Because functions are objects we can return a function from another function. In the below example, the create_adder function returns adder function.

# Python program to illustrate functions
# Functions can return another function

def create_adder(x):
    def adder(y):
        return x+y

    return adder

add_15 = create_adder(15)

print (add_15(10))

Output:

25