Functions in Python

A function is a block of organized, reusable code which only runs when it is called. You can pass data or parameters into a function.

Syntax to create a function:

def name_of_function(arg1,arg2,arg3):
    # Do coding here
    # Return statement

It begins with def followed by function name.

args1,args2,args3 are the arguments which are input to the function. Indentation is very important. Then you can write a code inside it.

Let’s see an example:

1. Print “hello world!”

def hello():                  #hello.py
    print('hello world!')
hello()     #call to a function
Output:
hello world!

2. Using parameters:

def hello(name):                  #hello.py
    print('hello',name)
hello('john') #calling a function
Output:
hello john

While calling hello function, we are passing ‘john’ as a parameter. ‘john’ will be copied into ‘name’ parameter of hello function and same is printed on console.

what if we don’t use parameter while calling a function ?

Let’s see…

def hello(name):                  #hello.py
    print('hello',name)
hello() #calling a function with no parameter
Output:
Traceback (most recent call last):
  File "/home/main.py", line 11, in <module>
    hello() #calling a function with no parameter
TypeError: hello() missing 1 required positional argument: 'name'

Let’s store the output of hello function hello into a variable.

def hello(name):                  #hello.py
    print('hello',name)
result=hello('john')    # storing output of hello function to result
print(result) 
print(type(result))    #printing the type of result
Output:
hello john
None
<class 'NoneType'>

What happened here ? ‘None’ is getting printed instead of ‘hello john’ .

Reason is function hello() is not returning any value and that’s why nothing is getting stored in result. Here, hello() function only printing a string. Now, question is, how to return value ?

Add ‘return’ statement at the end of function.

def hello(name):                  #hello.py
    print(name)
    return name        #returning a string 
result=hello('john')
print(type(result))
Output:
john
<class 'str'>

Let’s write a function to identify if the number prime or not.

def is_prime(num):
    for n in range(2,num):
        if num % n == 0:   
            print(num,'is not prime')
            break
    else: 
        print(num,'is prime!')
is_prime(17)
is_prime(4)
Output:
17 is prime!
4 is not prime!

return statement appears only once in a function as function execution ends when return statement is reached.

Now, You have basic understanding of writing your own function and reuse it!

Happy Coding!