How To Validate User Input In Python

Validating user input is a crucial step in ensuring the integrity and security of any application.

In Python, this process can be easily implemented with just a few lines of code. In this tutorial, we will learn how to validate user input in Python using basic techniques like checking that entered data matches specific criteria, such as length, format, or type.

Step 1: Get User Input

Let’s start by getting the user input. We will use the Python built-in function input() to get input from the user:

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user_input = input("Enter your data: ")

Step 2: Check The Input Length

Let’s say that the user input should have a minimum and maximum length. We can easily validate this using the len() function:

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min_length = 5
max_length = 10
 
if not min_length <= len(user_input) <= max_length:
    print("Error: input length must be between {} and {} characters.".format(min_length, max_length))

Step 3: Check The Input Format

It’s common to require that user input follow a specific format, such as including alphanumeric characters only. Let’s use Python’s str methods to check this:

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if not user_input.isalnum():
    print("Error: input must be alphanumeric.")

Step 4: Check The Input Type

Sometimes, we may expect the user to enter data of a specific type, such as an integer or float. To check the data type, we can use Python’s built-in functions int() and float() inside a try-except block to catch any inappropriate input:

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try:
    user_input = int(user_input)
except ValueError:
    print("Error: input must be an integer.")

Full Code

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min_length = 5
max_length = 10
 
user_input = input("Enter your data: ")
 
if not min_length <= len(user_input) <= max_length:
    print("Error: input length must be between {} and {} characters.".format(min_length, max_length))
elif not user_input.isalnum():
    print("Error: input must be alphanumeric.")
else:
    try:
        user_input = int(user_input)
    except ValueError:
        print("Error: input must be an integer.")
    else:
        print("User input accepted:", user_input)

Output

Enter your data: example123
User input accepted: 123

Conclusion

In this tutorial, we explored basic techniques for validating user input in Python. We focused on checking the input length, format, and type. Depending on your specific requirements, you can easily modify or expand upon these techniques to create a robust input validation system for your application.