Python Functions

 Block of reusable code to perform a specific action.

Reusing Code

Using an existing code without writing it every time we need.

Code

1

2

3

4

5

def greet():

print("Hello")

name = input()

print(name)

PYTHON

Input

Teja

Output

Teja

Defining a Function

Function is uniquely identified by the

function_name

Code

1

2

3

4

5

def greet():

print("Hello")

name = input()

print(name)

PYTHON

Input

Teja

Output

Teja

Calling a Function

The functional block of code is executed only when the function is called.

Code

1

2

3

4

5

6

def greet():

print("Hello")

name = input()

greet()

print(name)

PYTHON

Input

Teja

Output

Hello

Teja

Defining & Calling a Function

A function should be defined before it is called.

Code

1

2

3

4

5

6

name = input()

greet()

print(name)

def greet():

print("Hello")

PYTHON

Input

Teja

Output

NameError: name 'greet' is not defined

Printing a Message

Consider the following scenario, we want to create a function, that prints a custom message, based on some variable that is defined outside the function. In the below code snippet, we want to access the value in the variable

name

at line 2 in place of the

?

.

Code

1

2

3

4

5

6

def greet():

msg = "Hello " + ?

print(msg)

name = input()

greet()

PYTHON

Input

Teja

Desired Output

Hello Teja

We use the concept of Function Arguments for these types of scenarios.

Function With Arguments

We can pass values to a function using an Argument.

Code

1

2

3

4

5

6

def greet(word):

msg = "Hello " + word

print(msg)

name = input()

greet(word=name)

PYTHON

Input

Teja

Output

Hello Teja

Variables Inside a Function

A variable created inside a function can only be used in it.

Code

1

2

3

4

5

6

def greet(word):

msg = "Hello " + word

name = input()

greet(word=name)

print(msg)

PYTHON

Input

Teja

Output

NameError: name 'msg' is not defined

Returning a Value

To return a value from the function use

return

keyword.

Exits from the function when return statement is executed.

Code

1

2

3

4

5

6

7

def greet(word):

msg = "Hello " + word

return msg

name = input()

greeting = greet(word=name)

print(greeting)

PYTHON

Input

Teja

Output

Hello Teja

Code written after

return

statement will not be executed.

Code

1

2

3

4

5

6

7

8

def greet(word):

msg = "Hello "+word

return msg

print(msg)

name = input()

greeting = greet(word=name)

print(greeting)

PYTHON

Input

Teja

Output

Hello Teja

Built-in Functions

We are already using functions which are pre-defined in Python. Built-in functions are readily available for reuse

• print()
• int()
• str()
• len()