Adventures in Machine Learning

Mastering User Input Validation in Python: Best Practices and Examples

Float input is a ubiquitous feature of most programming languages. Programmers working with Python regularly have to handle float input from users, which involves receiving and validating input.

Handling invalid input is crucial and can determine whether the program runs smoothly or crashes on user input. The primary keywords used in this process include input(), float(), try/except, ValueError, and while loop.

In this article, we will cover how to handle float user input and restrict user input range.

Handling Float User Input

When receiving float user input in Python, the input() and float() functions are used. The input() function receives user input as a string, which can be converted to a float using the float() function.

For instance, if we want to receive a users height as input, the code will look like this:

height = float(input(“Enter your height in centimeters: “))

This code will display a prompt asking the user to enter their height in centimeters and return a float value. User input can be either valid or invalid, which is determined by the data type in use.

Handling Invalid Float Input

Invalid float input occurs when a user inputs data that cannot be interpreted as a floatfor example, when a user types a non-numerical value. To handle this, we can use a try/except statement.

The try/except clause ensures that the program doesn’t crash when invalid data is entered. The except block will be triggered if the user enters invalid input, and we can use this block to prompt the user again.

Heres an example:

while True:


height = float(input(“Enter your height in centimeters: “))


except ValueError:

print(“Invalid height. Try again.”)

In this example, a while True loop is used to keep prompting the user until valid input is entered.

If the user enters invalid input, the program tells them the input is invalid and continues to prompt them until valid input is received.

Prompting for Valid Float Input

Prompting the user for valid float input involves input validation. If a user enters invalid input, they will be prompted again for valid input.

A while loop can be used together with a continue or break statement to efficiently check the input and loop continuously until valid input is entered. The continue statement skips any code that follows it in the loop and prompts the user again, while the break statement exits the loop.

Heres how its done:

while True:

height = input(‘Enter your height in centimeters: ‘)

if ‘.’ not in height and not height.isnumeric():

print(“Invalid height entered, please try again”)


height = float(height)

print(‘Height entered is’, height, ‘cm.’)


In this case, the code ensures that the height entered is a valid float before converting it and exiting the loop. If the height entered is invalid, the continue statement will prompt the user to enter valid input again.

Restricting Float User Input Range

Sometimes, we want to restrict the user to input in a specific range, for example, accepting only input between two values. We can achieve this by combining a while loop, try/else statement, and a continue statement.

Heres how:

while True:


upper_bound = 10.0

lower_bound = 5.0

height = float(input(“Enter your height in centimeters: “))

if height < lower_bound or height > upper_bound:

print(“Height must be between”, lower_bound, “and”, upper_bound)



except ValueError:

print(‘Invalid height. Please try again.’)

The code above ensures that the input entered by the user falls between the specified upper and lower bounds.

If the input entered is outside this range, the program will prompt the user to input the value again.


Handling float user input and restricting the input range cannot be overemphasized with Python programming. The primary keywords used for input handling include input(), float(), try/except, ValueError, while loop, continue statement, and break statement.

By following the guidelines in this article, you can ensure your Python program runs smoothly without crashing based on user input. Python programming is a popular and versatile language used for developing applications and websites.

One essential aspect of programming in Python involves handling user input. Input validation is a crucial process in ensuring that a program runs smoothly and efficiently without crashing on user input.

In this article, we will delve deeper into handling user input, including the importance of handling exceptions, the different types of input errors, and additional resources available for learning more.

The Importance of Handling Exceptions

When handling user input in Python, it is essential to consider the possibility of an input error occurring. For instance, a user may input a non-numeric value when a numeric value is expected.

When input errors occur, it is crucial to handle these exceptions gracefully without crashing the program. Python provides two primary approaches to handle exceptions: using the try-except statement or using the if-else statement.

The try-except statement is a block of code used to handle exceptions in Python. With the try-except statement, Python will evaluate the code within the try section.

If an exception occurs, the code within the except section is executed. Here is an example of a simple try-except statement:


age = int(input(“Please enter your age: “))


print(“Invalid input.

Please enter a number.”)

In this example, the code tries to convert the input into an integer. If it is unsuccessful in doing so, the except block prints an error message.

In contrast, the if-else statement checks conditions before executing code:

age = input(“Please enter your age: “)

if age.isdigit():

age = int(age)


print(“Invalid input. Please enter a number.”)

In this example, the code first checks if the input is a digit.

If it is, the input is converted to an integer. Otherwise, an error message is printed.

Both approaches are useful and can be used interchangeably depending on the needs of the program.

Different Types of Input Errors

There are different types of input errors that can occur when dealing with user input in Python. Some of these input errors include:


Non-Numeric Input This error occurs when a user inputs a non-numeric value, like “hello,” when a numeric value is expected. 2.

Non-Printable Characters This error occurs when a user inputs characters that are not printable. These characters include control characters, non-printable spaces, and other casing issues.

3. Empty String This error occurs when a user submits an empty string and does not provide a value.

4. Out-of-Range Values This error occurs when a user inputs values that are out of the specified range.

To handle these errors, it is essential to implement input validation in your program. Input validation enables the program to check if input data meets certain criteria before processing it.

Additional Resources

There are numerous resources for learning more about how to handle user input in Python. Below are some of the best resources available:


The Python Documentation The official Python documentation provides detailed information about input handling, including reference guides, tutorials, and sample code. 2.

Codecademy Codecademy is an online platform that offers interactive coding lessons in Python. The site provides a comprehensive course on Python programming that includes input validation.

3. Python for Everybody Python for Everybody is a free online course offered by the University of Michigan.

The course provides a comprehensive introduction to Python programming and covers input validation. 4.

Stack Overflow Stack Overflow is a popular Q&A platform for programmers. It provides a platform for asking and answering Python-specific questions related to input validation.

5. Real Python Real Python is an online community that offers customized Python courses, tutorials, webinars, and other resources on various Python-related topics, including input handling.


In conclusion, handling user input is a vital component in ensuring that Python programs run smoothly. It is crucial to validate user input to prevent errors and crashes.

Python provides different approaches to handle exceptions, including try-except statements and if-else statements. Additionally, identifying potential input errors can help in understanding how to handle these errors.

Finally, there are several resources available to programmers who want to learn more about handling user input in Python, including the official Python documentation, online courses, and other online resources. Handling user input is a crucial aspect of programming and prevents errors and crashes.

Main points in this article include using the try-except or if-else statements to handle exceptions, identifying potential input errors, and further resources available for learning more. Proper input validation through error handling prevents issues in Python programs with user input and can also enhance user experience.

It is also essential to keep learning and improving on this topic since new errors and issues may come up. As a programmer, these strategies are foundational, and being proficient at input validation will make a significant difference in building reliable, easy-to-use applications and websites.

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