Basic query about python loop

Question

So , I have this code snippet :

import sys

while True:
  print("Make sure the number of digits are exactly 12 : ")
  x = input()
  if str(x) == 12:
      break

  code = []

  for i in range(12):
      code[i] = int(x[i])

I want the program to repeat the lines , "Make sure .... 12 :" if 12 digits are not inputed. After that , I am copying them to an array to access each individual element of it to do very basic arithmetic calculations . Am I going in the right direction ? I am totally new to python , how can I fix this ? The above code is showing the following error .

Traceback (most recent call last):
  File "C:\Users\Arjo\Desktop\hw2a.py", line 14, in <module>
    code[i] = int(x[i])
IndexError: list assignment index out of range

Explosion Pills · Accepted Answer · 2013-02-08 03:41:25Z

3

You're not creating an array of inputs with x, but rather overwriting it each time. Your comparison is also wrong; you don't want to see that the string of x is, 12, but that it has a length of 12:

x = []
while True:
  print("Make sure the number of digits are exactly 12 : ")
  x.append(input())
  if len(x) == 12:
      break

answered Feb 8, 2013 at 3:41

Explosion Pills

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5 Comments

John La Rooy Over a year ago

Are you sure you want to break when the length of x is 12?

Explosion Pills Over a year ago

@gnibbler I think so .. why?

John La Rooy Over a year ago

The way the code is indented now, all of the stuff about code will be skipped

Explosion Pills Over a year ago

@gnibbler true, I didn't consider that; it should probably be dedented then

John La Rooy Over a year ago

Depends on the intent of the while loop. If there is supposed to be just one input processed the part under the break should be dedented.

John La Rooy · Accepted Answer · 2013-02-08 04:01:35Z

1

IndexError: list assignment index out of range is occuring because you have an empty list and are trying to update the first element. Since the list is empty there is no first element, so the exception is raised.

One way to correct this problem is to use code.append(x[i]) but there is an easier way in this case. The default list constructor will do exactly what you want

I think you probably want something like this

while True:
  print("Make sure the number of digits are exactly 12 : ")
  x = input()
  if len(x) != 12:   # if the length is not 12
      continue       # ask again

  code = list(x)

This will keep asking for more input until exactly 12 characters are entered

edited Feb 8, 2013 at 4:01

answered Feb 8, 2013 at 3:56

John La Rooy

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2 Comments

thestralFeather7 Over a year ago

so i won't need to use the for loop part at all then ? , how should I access the individual elements in code array ? . Also , we can skip this line then code = [] ?

John La Rooy Over a year ago

@novice7, you don't need the code = [] line. You access the elements as you were code[i] where i is bewteen 0 and 11

hd1 · Accepted Answer · 2013-02-08 03:42:06Z

0

No, this doesn't look like it will work... Try changing this:

if str(x) == 12:
      break

into this:

if len(str(x)) == 12: 
    break

Hope that helps...

answered Feb 8, 2013 at 3:42

hd1

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