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Engineering LibreTexts

2.10: Asking the user for input

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  • Sometimes we would like to take the value for a variable from the user via their keyboard. Python provides a built-in function called input that gets input from the keyboard1. When this function is called, the program stops and waits for the user to type something. When the user presses Return or Enter, the program resumes and input returns what the user typed as a string.

    >>> inp = input()
    Some silly stuff
    >>> print(inp)
    Some silly stuff

    Before getting input from the user, it is a good idea to print a prompt telling the user what to input. You can pass a string to input to be displayed to the user before pausing for input:

    Code \(\PageIndex{1}\) (Python):

    name = input('What is your name?\n')

    The sequence \n at the end of the prompt represents a newline, which is a special character that causes a line break. That's why the user's input appears below the prompt.

    If you expect the user to type an integer, you can try to convert the return value to int using the int() function:

    Code \(\PageIndex{2}\) (Python):

    prompt = ' the airspeed velocity of an unladen swallow?\n'
    speed = input(prompt)
    int(speed) + 5

    But if the user types something other than a string of digits, you get an error:

    >>> speed = input(prompt) the airspeed velocity of an unladen swallow?
    What do you mean, an African or a European swallow?
    >>> int(speed)
    ValueError: invalid literal for int() with base 10:

    We will see how to handle this kind of error later.