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) 

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