Python ValueError Exception Handling Examples

Python ValueError is raised when a function receives an argument of the correct type but an inappropriate value. Also, the situation should not be described by a more precise exception such as IndexError.

You will get ValueError with mathematical operations, such as square root of a negative number.

>>> import math
>>> 
>>> math.sqrt(-10)
Traceback (most recent call last):
  File "<stdin>", line 1, in <module>
ValueError: math domain error
>>> 

Here is a simple example to handle ValueError exception using try-except block.

import math
x = int(input('Please enter a positive number:\n'))
try:
    print(f'Square Root of {x} is {math.sqrt(x)}')
except ValueError as ve:
    print(f'You entered {x}, which is not a positive number.')

Here is the output of the program with different types of input.

Please enter a positive number:
16
Square Root of 16 is 4.0
Please enter a positive number:
-10
You entered -10, which is not a positive number.
Please enter a positive number:
abc
Traceback (most recent call last):
  File "/Users/pankaj/Documents/PycharmProjects/hello-world/journaldev/errors/valueerror_examples.py", line 11, in <module>
    x = int(input('Please enter a positive number:\n'))
ValueError: invalid literal for int() with base 10: 'abc'

Our program can raise ValueError in int() and math.sqrt() functions. So, we can create a nested try-except block to handle both of them. Here is the updated snippet to take care of all the ValueError scenarios.

import math
try:
    x = int(input('Please enter a positive number:\n'))
    try:
        print(f'Square Root of {x} is {math.sqrt(x)}')
    except ValueError as ve:
        print(f'You entered {x}, which is not a positive number.')
except ValueError as ve:
    print('You are supposed to enter positive number.')

Here is a simple example where we are raising ValueError for input argument of correct type but inappropriate value.

import math
def num_stats(x):
    if x is not int:
        raise TypeError('Work with Numbers Only')
    if x < 0:
        raise ValueError('Work with Positive Numbers Only')
    print(f'{x} square is {x * x}')
    print(f'{x} square root is {math.sqrt(x)}')

• Python Exception Handling
• ValueError Python Docs