How to Fix ValueError Exceptions in Python

The Python ValueError is an exception that occurs when a function receives an argument of the correct data type but an inappropriate value. This error usually occurs in mathematical operations that require a certain kind of value.

What Causes ValueError

The Python ValueError is raised when the wrong value is assigned to an object. This can happen if the value is invalid for a given operation, or if the value does not exist. For example, if a negative integer is passed to a square root operation, a ValueError is raised.

Python ValueError Example

Here’s an example of a Python ValueError raised when trying to perform a square root operation on a negative number:

import math

math.sqrt(-100)

In the above example, a negative integer is passed to the math.sqrt() function. Since the function expects a positive integer, running the above code raises a ValueError:

Traceback (most recent call last):
  File "test.py", line 3, in <module>
    math.sqrt(-100)
ValueError: math domain error

How to Fix ValueError Exceptions in Python

To resolve the ValueError in Python code, a try-except block can be used. The lines of code that can throw the ValueError should be placed in the try block, and the except block can catch and handle the error.

Using the above approach, the previous example can be updated to handle the error:

import math

try:
    math.sqrt(-100)
except ValueError:
    print('Positive number expected for square root operation')
    

Here, a check is performed for the ValueError using the try-except block. When the above code is executed, the except block catches the ValueError and handles it, producing the following output:

Positive number expected for square root operation

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