python program behaves differently in python shell vs terminal

Question

I have a simple Python program that asks yes or no question and I validate that input. If I run this Python shell, it runs fine. If I enter invalid characters it loops back to top of while.

However, if I run this in the terminal window and try to enter an invalid character it errors as shown below.

endProgram = 0
while endProgram != 1:
    userInput = input("Yes or No? ");
    userInput = userInput.lower();

    while userInput not in ['yes', 'no']:
        print("Try again.")
        break

    endProgram = userInput == 'no'

enter image description here

Are you using the same Python version on both? input changes behavior between 2 and 3. — tzaman
– tzaman, Commented May 7, 2015 at 2:42

tzaman · Accepted Answer · 2015-05-07 02:47:32Z

4

Looks like your RPi is using Python 2; the input function does an eval there.
input in Python 3 is equivalent to raw_input in Python 2. (See PEP-3111)

Ideally, you should change your RPi interpreter to Python 3. Failing that, you can make it version-agnostic like so:

try:
    input = raw_input
except NameError:
    pass

answered May 7, 2015 at 2:47

tzaman

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wim · Accepted Answer · 2015-05-07 02:48:40Z

3

I can clearly see in the interactive shell you working in python 3.2.3 (background). But I can not see the python version you're running from the command line (foreground).

On your raspberrypi, execute this command from the shell:

python --version

I am expecting to see python 2.x here, because the behaviour of input() differs between python 2 and python 3, in a way that would cause exactly the behaviour you have seen.

You might want to add a line like

#!/usr/bin/env python3

To the top of your .py file, and then chmod +x on it. Afterward you should be able to execute it directly (./guipy01.py) and the correct python interpreter will be selected automatically.

edited May 7, 2015 at 2:48

answered May 7, 2015 at 2:43

wim

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