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raise keyword with example in Python

Python raise keyword: Here, we are going to learn about the raise keyword with example.
Submitted by IncludeHelp, on April 14, 2019

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)

Output

First run:
Enter a positive number: 20
num =  20

Second run:
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)

Output

First run:
Input a string: IncludeHelp
The input was:  IncludeHelp

Second run:
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:
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