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For a practice problem in my homework, i'm making a guessing game that starts off by asking for a number. I'm trying to implement a way that prints "invalid input" when given a string, but i get an error message. here is my code:

def get_input():
    '''
    Continually prompt the user for a number, 1,2 or 3 until
    the user provides a good input. You will need a type conversion.
    :return: The users chosen number as an integer
    '''
    guess=int(input("give me 1,2,3"))
    while True:
        if guess==1 or guess==2 or guess==3:
            return guess
        else:
            print "Invalid input!"

        guess=int(input("give me 1,2,3"))

I get this message when I put in a string such as 

hello/System/Library/Frameworks/Python.framework/Versions/2.6/bin/python2.6 /Users/bob/PycharmProjects/untitled/warmup/__init__.py

give me 1,2,3hello

Traceback (most recent call last):
  File "/Users/bob/PycharmProjects/untitled/warmup/__init__.py", line 51, in <module>
    get_input()
  File "/Users/bob/PycharmProjects/untitled/warmup/__init__.py", line 43, in get_input
    guess=int(input("give me 1,2,3"))
  File "<string>", line 1, in <module>
NameError: name 'hello' is not defined

Process finished with exit code 1
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3
  • You may use try catch for this scenario. Commented Oct 3, 2015 at 18:43
  • 1
    Possible duplicate of Python input() error - NameError: name '...' is not defined Commented Oct 3, 2015 at 18:46
  • input('enter an integer') and raw_input('enter a string') Commented Oct 3, 2015 at 19:07

2 Answers 2

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5

You need to use raw_input for python2, input tries to evaluate the string so it looks for a variable called name and errors as there is no variable called name defined anywhere. You should never use input in python2, it is equivalent to eval(raw_input()) which has obvious security risks.

So to spell it out more clearly, don't use input to take input from a user in python2, use raw_input() and in your case take the raw_input using a try/except catching a ValueError. 

def get_input():
    '''
    Continually prompt the user for a number, 1,2 or 3 until
    the user provides a good input. You will need a type conversion.
    :return: The users chosen number as an integer
    '''

    while True:
        try:
            guess = int(raw_input("give me 1,2,3"))
            if guess in (1, 2, 3):
                return guess
        except ValueError:
            pass
        print("Invalid input!")

The fact you are just cheking for 1,2 or 3 means you could also just do the casting after you confirm:

def get_input():
    '''
    Continually prompt the user for a number, 1,2 or 3 until
    the user provides a good input. You will need a type conversion.
    :return: The users chosen number as an integer
    '''

    while True:
        guess = raw_input("give me 1,2,3")
        if guess in ("1", "2", "3"):
            return int(guess)
        print("Invalid input!")
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5 Comments

this will solve the problem but it looks more like a comment then an answer
@VigneshKalai, this is the answer to the question, input accepts integer but crashes on a string,what do you think is causing that?
I am not saying you're answer is wrong it is just that you could add a link stating about this behaviour of the input method
Answered the question! Now you've added code, just one comment doesn't print "Invalid Input" for int inputs < 1 or > 4, you could just pass on the exception and print if it loops (given the return exits the loop).
@achampion, True, easier just to pass and print.
1

You should to verify the input type before converting into a int:

guess = raw_input("give me 1,2,3")

while True:
   if guess == '1' or guess == '2' or guess == '3':
      return int(guess)
   else:
      print "Invalid input!"

   guess = raw_input("give me 1,2,3")
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12 Comments

raw_input always returns a string, gess doesn't exist and else: pass is completely useless.
@gre_gor you're right, i was a bit distracted. i assume my mistake here, sorry.
Now you are using is to test for equality, not a good idea! Also else:pass is redundant.
yep. is would work at least using cpython but it is an implementation detail that should never be relied upon. is should be used for identity, == to test if two values are equal not necessarily the same object in memory
@gre_gor is a suggestion to pass the input to function arg. Thx Padraic.
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