How to Execute Input Validation in Python

1. Use the try...except Statement to Check if the User Input Is Valid in Python
2. Uses the isdigit() Function to Check if the User Input Is Valid in Python

Input validation can be defined as the process of checking if the input provided by the user from the input() function is both valid and acceptable in a given case or scenario.

In this article, you’ll learn how to check if the user input is valid in Python.

Use the try...except Statement to Check if the User Input Is Valid in Python

The try...except statement is utilized for the purpose of exception handling in Python. The try...except statement is divided into three blocks, all of which have different uses.

• The try block contains the cluster of code to be tested for any errors.
• The except block is used to add exceptions and handle the errors of the code.
• The finally block contains the statements that need to be executed; it’s ignored by the try and except blocks.

To explain input validation in Python, we will take a program where the user is asked for input using the built-in input() function in Python.

The following code implements the try...except statement to check if the user input is valid in Python.

while True:
    try:
        dage = int(input("Enter your age: "))
    except ValueError:
        print("This is an unaccepted response, enter a valid value")
        continue
    else:
        break
if dage >= 21:
    print("You're the legal age to drink in India")
else:
    print("You're not the legal age to drink in India")

Output:

Enter your age: eight
This is an unaccepted response, enter a valid value
Enter your age: 8
You're not the legal age to drink in India

In the code above, the try block contains the input function and sets the parameter that the value the user will input should be an int. Then, the except block handles the error. Python allows us to define as many except blocks as we want in a chunk of code.

The output shows the error message of the except block when any other value is inputted, instead of an int value. The latter part of the program is easy and uses the if-else statement to check whether a person is at a legal drinking age or not.

Uses the isdigit() Function to Check if the User Input Is Valid in Python

The isdigit() function can be utilized to check whether the value provided of an input is a digit (0-9) or not. It returns a True value if the string contains numeric integer values only; it does not consider floating-point numbers.

The following code executes the user-defined function that uses the isdigit() function to check if the user input is valid in Python.

def check1(num):
    if num.strip().isdigit():
        print("The Input is Number")
    else:
        print("The Input is string")


x = input("Enter your age:")
check1(x)

Output:

Enter your age:18
The Input is Number

The user-defined function is created just to check whether the user input received is a number or a string.