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