Python: raw_input asks for input once the first time, then twice

Question

I ran across this old piece of code on my PC:

# -*- coding: utf-8 -*-

player_pos = 2

def game():
    global player_pos

    background = [2, 1, 2, 1, 2]
    screen     = [0] * 5

    for i in range(5):
        screen[i] = background[i]

    screen[player_pos] = 7

    print screen

    if raw_input("> ") == 'a':
        player_pos -= 1

    elif raw_input("> ") == 'd':
        player_pos += 1

while True:
    game()

I run it from IDLE and the prompt works as expected. However, if you press 'a' or 'd', it may work properly or just print a blank line, and then work properly if you press 'd' again. So you need to press 'a' or 'd' once or twice, and I want it to always be once.

I found this question but I don't know how to translate it to my problem. Simple:Python asks for input twice

there's not a lot of translation to do to apply this to your problem. every time you do `raw_input()` you're prompting the user for input. instead, store `raw_input` in a variable before your `if` and `elif`, then test the variable. — Zev Averbach, Jan 28 '15 at 16:49
possible duplicate of [Why while loop is sticking at raw\_input? (python)](http://stackoverflow.com/questions/13267107/why-while-loop-is-sticking-at-raw-input-python) — Zev Averbach, Jan 28 '15 at 16:51
in your code, inputing `d` requires inputing anything but `a` first, and then `d`. — njzk2, Jan 28 '15 at 16:56

score 3 · Accepted Answer · answered Jan 28 '15 at 16:46

3

You are calling the raw_input method twice - once in each if statement. You could store the user input in a local var and then test it:

user_answer = raw_input("> ")
if user_answer == 'a':
    player_pos -= 1
elif user_answer == 'd':
    player_pos += 1

answered Jan 28 '15 at 16:46

El Bert

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Exactly what i'd post. – rafaeldefazio Jan 28 '15 at 16:47

score 0 · Answer 2 · answered Jan 28 '15 at 16:58

Run this step by step:

raw_input is called, the user's input is read.
this input is compared to a.
if it is not a, raw_input is called again, the user's input is read.
this new input is compared to d.

As you can see, to input d, you must first not input a, as raw_input is called twice.

Python: raw_input asks for input once the first time, then twice

2 Answers2