raise keyword with example in Python

Python raise keyword

except is a keyword (case-sensitive) in python, it is used to raise an Exception/Error with a customized message and stops the execution of the programs.

It is very useful when you want to work with the input validations. For example – if you are working with the positive numbers and someone inputs a negative number, in this case, we can raise an error and stop the program’s execution.

Syntax of raise keyword:

if test_condition:
    raise Exception(Message)

Example:

Input:
string = "Hello"

if string=="Hello" or string=="Hi" or string=="Bye":
    raise Exception("This word is not allowed")

Output:
Exception: This word is not allowed

Python examples of raise keyword

Example 1: Input a positive number and raise an exception if input is a negative value .

# python code to demonstrate example of
# raise keyword

# Input a positive number and raise an exception
# if input is a negative value

num = int(input("Enter a positive number: "))

if num<0:
    raise Exception("Please input only positive value ")

print("num = ", num)

First run:

OUTPUT :

Enter a positive number: 20

num = 20

Second run:

OUTPUT :

Enter a positive number: -10

Traceback (most recent call last):

File “/home/main.py”, line 10, in <module>

raise Exception(“Please input only positive value “)

Exception: Please input only positive value

Example 2: Input a string and raise an exception on specific words.

# python code to demonstrate example of
# raise keyword

# Input a string and raise an exception on specific words

string = input("Input a string: ")

# words - we are checking
# 'Hello', 'Hi' or 'Bye'
if string=="Hello" or string=="Hi" or string=="Bye":
    raise Exception("This word is not allowed")

print("The input was: ", string)

First run:

OUTPUT :

Input a string: IncludeHelp

The input was: IncludeHelp

Second run:

OUTPUT :

Input a string: Hello

Traceback (most recent call last):

File “/home/main.py”, line 11, in <module>

raise Exception(“This word is not allowed”)

Exception: This word is not allowed

Third run:

OUTPUT :

Input a string: Bye

Traceback (most recent call last):

File “/home/main.py”, line 11, in <module>

raise Exception(“This word is not allowed”)

Exception: This word is not allowed