How can I limit the user input to only integers in Python

I’m trying to make a multiple choice survey that allows the user to pick from options 1-x. How can I make it so that if the user enters any characters besides numbers, return something like “That’s an invalid answer”

def Survey():
    print('1) Blue')
    print('2) Red')
    print('3) Yellow')
    question = int(input('Out of these options(1,2,3), which is your favourite?'))
    if question == 1:
        print('Nice!')
    elif question == 2:
        print('Cool')
    elif question == 3:
        print('Awesome!')
    else:
        print('That's not an option!')

Answers:

Thank you for visiting the Q&A section on Magenaut. Please note that all the answers may not help you solve the issue immediately. So please treat them as advisements. If you found the post helpful (or not), leave a comment & I’ll get back to you as soon as possible.

Method 1

Your code would become:

def Survey():

    print('1) Blue')
    print('2) Red')
    print('3) Yellow')

    while True:
        try:
            question = int(input('Out of these options(1,2,3), which is your favourite?'))
            break
        except:
            print("That's not a valid option!")

    if question == 1:
        print('Nice!')
    elif question == 2:
        print('Cool')
    elif question == 3:
        print('Awesome!')
    else:
        print('That's not an option!')

The way this works is it makes a loop that will loop infinitely until only numbers are put in. So say I put ‘1’, it would break the loop. But if I put ‘Fooey!’ the error that WOULD have been raised gets caught by the except statement, and it loops as it hasn’t been broken.

Method 2

The best way would be to use a helper function which can accept a variable type along with the message to take input.

def _input(message, input_type=str):
    while True:
      try:
        return input_type (input(message))
    except:pass

if __name__ == '__main__':
    _input("Only accepting integer : ", int)
    _input("Only accepting float : ", float)
    _input("Accepting anything as string : ")

So when you want an integer , you can pass it that i only want integer, just in case you can accept floating number you pass the float as a parameter. It will make your code really slim so if you have to take input 10 times , you don’t want to write try catch blocks ten times.

Method 3

def func():
    choice = "Wrong"
    
    while choice.isdigit()==False :
        choice = input("Enter a number: ")
        
        if choice.isdigit()==False:
            print("Wrongly entered: ")
        else:
            return int(choice)

Method 4

One solution amongst others : use the type function or isinstance function to check if you have an ̀int or a float or some other type

>>> type(1)
<type 'int'>

>>> type(1.5)
<type 'float'>

>>> isinstance(1.5, int)
False

>>> isinstance(1.5, (int, float))
True

Method 5

I would catch first the ValueError (not integer) exception and check if the answer is acceptable (within 1, 2, 3) or raise another ValueError exception

def survey():
    print('1) Blue')
    print('2) Red')
    print('3) Yellow')

    ans = 0
    while not ans:
        try:
            ans = int(input('Out of these options(1, 2, 3), which is your favourite?'))
            if ans not in (1, 2, 3):
                raise ValueError
        except ValueError:
            ans = 0
            print("That's not an option!")

    if ans == 1:
        print('Nice!')
    elif ans == 2:
        print('Cool')
    elif ans == 3:
        print('Awesome!')
    return None

Method 6

You can use a module Named PyInputPlus

Installation

pip install PyInputPlus

You can use this as

def Survey():
    print('1) Blue')
    print('2) Red')
    print('3) Yellow')
    question = int(input('Out of these options(1,2,3), which is your favourite?'))
    if question == 1:
        print('Nice!')
    elif question == 2:
        print('Cool')
    elif question == 3:
        print('Awesome!')
    else:
        print('That's not an option!')# answered after 7 years

Method 7

I made a module for cases like this called restricted_input which checks the input in real time. Here, since you only need inputs from 1-3, this would do

from restricted_input import r_input
num = int(r_input("Out of these options(1,2,3), which is your favourite? ", input_type="nothing", allow="123", maxlength=1))

It uses msvcrt.getch/termios to get non-blocking input, so it checks it in real time and allows only the specified characters.
Note: This will not work in IDLEs like Spyder, Jupyter etc.

All methods was sourced from stackoverflow.com or stackexchange.com, is licensed under cc by-sa 2.5, cc by-sa 3.0 and cc by-sa 4.0