ValueError Exception in Python

#import the math module
import math

print(math.sqrt(-4))

A ValueError exception is raised  when an inappropriate value but which is of correct type is used in an operation.

For example, consider what happens when we try to find the square root of a negative real number. The number is surely an integer but its square root is undefined , in such a case, Python raises a ValueError.

The most common cause of ValueError exception is when  we pass an inappropriate value to a function, but which is of supported type. 

#In the example below a value error is raised

print(int("10"))

print(int("a"))

In the above example, a ValueError is raised because while the builtin int() functions takes string arguments, string "a" cannot be converted to an integer representation. 

ValueError and Unpacking

Retrieving elements from an iterable and assigning them to variables is referred to as "Unpacking". In such a case, a ValueError is raised if the number of variables do not match the number of items in the argument. This is because in such  cases, Python can't  tell which value to assign to which variable.

a, b  = [1, 2]
print(a, b)

#this raises a ValueError
a, b = [1, 2, 3]

What is the difference between ValueError and TypeError?

ValueError and TypeError exceptions are closely linked  in that they both indicate when an incorrect data type has been used. ValueError occurs when  an operation or a function receives an argument of the correct type, but an inappropriate value; TypeError occurs when an operation or function is applied to an object of an incorrect type.

import math

math.sqrt(-8)

import math

math.sqrt("-8")

Handling ValueError exceptions

To handle the ValueError exception, you can use try and except blocks to catch the error and proceed accordingly.

#import the math module
import math

try:

   math.sqrt(-10)

except ValueError:
    print("bad argument given")
 

#Define function "interactive_add" that returns sum of two integers entered by user
def interactive_add():
    try:
        x = int(input("Enter an integer:"))
        y = int(input("Enter an integer:"))
        
        print("{} + {} = {}".format(x, y, x + y))
    
    except ValueError:
        print("You did not enter an integer!")

#Call the function
interactive_add()
//Enter an integer: 7
//Enter an integer: "Hello!"
//You did not enter an integer!