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.

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

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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.

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# 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)

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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.

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# 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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