How to Fix the Python ValueError

Python ValueError is an error that occurs when a programmer using the Python programming language (PPL) passes a function an erroneous value even though it is an acceptable argument. It will be easier for you to create many running Python programs if you understand what a Python ValueError is, how to identify it, and how to fix it.

This article describes the Python ValueError, its causes, how to identify it, and how to fix each Value Error in Python.

Python ValueError Overview

Before we look at what the Python ValueError is, there are two concepts that we need to understand. One of those terms was introduced in the section above, argument.

A parameter and an argument are two different terms. According to the difference between an argument and a parameter article, when creating functions, we provide specific inputs in order to carry out the function's instructions. In other words, we refer to these inputs as "arguments" or "parameters” interchangeably.

In Python programming language (PPL), we can make a summary of differences between A parameter and an argument in the following table:

#	Arguments	#	Parameters
1	In PPL, we convey the value from the calling function to the receiving function using variables in the function.	1	When we define a function in PPL, the parameters are defined as well.
2	In PPL function call statements, we use the parameters to pass values from the caller function to the receiving function.	2	In PPL, we use the local variables in the function declaration to obtain the value from the arguments.
3	In PPL, each argument is always assigned to a parameter in the function definition at the time of the call.	3	In PPL, when we invoke the function, the values of the arguments are assigned to the local variables.
4	Actual parameters are another name for the arguments.	4	They have other names as Formal Parameters.

The Python ValueError occurs when a function receives a correct argument but an inappropriate value. For example, if you have a square root function and you input the negative number, the argument is valid but the value is invalid. In this case, the PPL raises a ValueError message.

We'll examine the definition of ValueError in PPL in the section after that.

What is ValueError in Python?

We can infer from the name of the problem that a ValueError happens when a value input is incorrect. As we saw in the section above, errors frequently occur when performing the mathematical operations required to carry out the function.

For instance, the built-in Python method int() outputs an integer number, but if you enter a string, it will raise a ValueError warning in PPL.

We can see the causes of this PPL error after understanding what Python ValueError is.

What Causes Python ValueError

Based on the above sections: ValueError introduction, overview, and ValueError meaning, Python ValueError causes can be divided into two groups. The first is that the value entered is wrong and the second is that the value input does not exit. The PPL will issue a ValueError error in any scenario.

We will use the examples in the following section to illustrate each cause of ValueError in Python.

Python ValueError Examples

We will use the examples in the following section to illustrate each cause of ValueError in Python.

The square root of a positive number is calculated using a function that we build. However, we will receive the ValueError notice if we enter a negative number.

Example1 for ValueError in python:

# A function that return a square root of a positive number
import math as mt
def Square_root(number):
    ''' Returns a square root of a number '''
    return round(mt.sqrt(number),2)
# Call the function
def main():
    number = -33
    result = Square_root(number)
    print(result)
if __name__ == "__main__":
   main()

Due to the fact that a square root takes a positive number, the code above returns a ValueError which is seen below:

ValueError Example1

We need to correct the value input and then get the results in the following code.

Example1 for ValueError Fixed in python:

# A function that return a square root of a positive number
import math as mt
def Square_root(number):
    ''' Returns a square root of a number '''
    return round(mt.sqrt(number),2)
# Call the function
def main():
    number = 33
    result = Square_root(number)
    print(result)
if __name__ == "__main__":
   main()
# Output is 5.74

The logarithm function has the domain of definition of positive numbers, that is \(\forall x>0\). However, we will receive the ValueError notice if we enter a zero or a negative number.

Example2 for ValueError in python:

# A function that returns a logarithm of a positive number
import math as mt
def Logarithm(number):
    ''' Returns a logarithm of a number '''
    return round(mt.log(number),2)
# Call the function
def main():
    number = -33
    result = Logarithm(number)
    print(result)
if __name__ == "__main__":
   main()

Due to the fact that a logarithm function takes a positive number, the code above returns a ValueError which is seen below:

ValueError Example1

By using the correct value input, we get the results below:

Example2 for ValueError Fixed in python:

# A function that returns a logarithm of a positive number
import math as mt
def Logarithm(number):
    ''' Returns a logarithm of a number '''
    return round(mt.log(number),2)
# Call the function
def main():
    number = 33
    result = Logarithm(number)
    print(result)
if __name__ == "__main__":
   main()
#Output is 3.5

How to Fix ValueError in Python

The Python ValueError Exception is another name for this. By taking note of the following, we can correct this mistake:

1. In PPL, we can use try-except block to handle ValueError exception.
2. In PPL, ValueError is raised in a lot of mathematical operations in the math module.
3. We can raise ValueError in a function if it works for only specific range of values in Python programmming language.

Let us use the above example 1 to handle the existing of the ValueError in Python.

Try-Except Block to Fix ValueError in Python:

# A function that return a square root of a positive number
# With try-except block to fix ValueError
import math as mt
def Square_root(number):
    ''' Returns a square root of a number '''
    try:
        result = round(mt.sqrt(number),2)
        print(result)
    except ValueError:
        print('A Positive number expected for square root operation')
# Call the function
def main():
    number = -33
    result = Square_root(number)
if __name__ == "__main__":
   main()

The output is shown in the below image:

ValueError Fixing

Conclusion

This article's main objective was to fix Python ValueError. We discussed the distinction between a parameter and an argument. We have seen also the possible causes of this Python value input error. To fix this Python error, we finally utilize a try-except block in the function.

Other Python Errors and Exceptions

Messages known as Python errors and exceptions are shown when a program encounters an unexpected event. They provide information about the error that has happened and can assist in identifying the issue and locating a solution. These are some additional Python errors and exceptions that we have already covered.

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