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How to take Float user input in Python

Collecting float values from user input is a common task in interactive Python applications.

This guide explores different methods for obtaining float input, including input validation, error handling, and range checking. You'll learn how to ensure your programs receive valid float values.

Basic Float Input with float()​

The most straightforward approach to take float input is by using the input() function to get the input from the user, and then immediately converting that input to a float using the float() constructor.

user_input = float(input('Enter a float: '))
print(user_input)

The input() function always returns a string. The float() constructor then attempts to convert the returned string into a float.

Handling ValueError Exceptions​

If the user enters a non-numeric string that can not be converted to a float, the float() constructor raises a ValueError. Use a try/except block to handle this situation:

try:
    user_input = float(input('Enter a float: '))
    print(user_input)
except ValueError:
    print('Enter a valid float')
  • The try block contains the code which can potentially throw an exception.
  • The except ValueError block handles the ValueError exception that is raised if the input can not be converted to a float.

Validating Input with a Loop​

To ensure that the user only enters valid float input, embed the try/except block in a while loop:

while True:
    try:
        num = float(input("Enter your favorite float: "))
    except ValueError:
        print("Please enter a valid float")
        continue
    else:
        print(f'You entered: {num}')
        break

Explanation:

  • A while True loop will continue prompting for input.
  • If a ValueError is raised in the try block, an error message is displayed and the loop continues with the continue statement.
  • If a valid float is entered, the else block runs and the program displays a confirmation message and uses the break statement to exit the loop.

Limiting Input to a Specific Range​

You can add range checking using an if statement inside the else block. This way you can force the user to only enter a float within a specific range.

while True:
    try:
        num = float(input("Enter a float 1.1-9.9: "))
    except ValueError:
        print("Please enter a valid float 1.1-9.9")
        continue
    if 1.1 <= num <= 9.9:
        print(f'You entered: {num}')
        break
    else:
        print('The float must be in the range 1.1-9.9')

Explanation:

  • The try/except block remains the same.
  • An if statement checks whether the input is within the specified range using boolean operators (>= and <=). If it is in range the program will display a confirmation message and exit the loop.
  • If the number is not within the specified range, the else block displays an error and prompts the user for input again.

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