How to test a string as a list of integers Python

Question

So im trying to accept input of an RGB color values,which means they have to be integers within 0-255,such as:

123,245,230

but i want to make sure that they have formatted it correctly, so i'm taking the input as a string and im trying to force it into a list. my original solution was

    colorList=colorListString.split(",")
    for i in range(3):
        colorList[i]=int(colorList[i])
    colorMatrix+=[colorList]

but this doesn't make sure that there is always 3 values, so i complicated it to first make sure that the input was 3 values determined with

   while colorListString.count(",") !=2: 
        print("Color number ",x+1,": ")
        colorListString=input()

but now im running into the problem that i dont know how to make sure that the three values are indeed integers, and keep that neatly within the while loop

Possible duplicate of [Checking whether a variable is an integer or not](https://stackoverflow.com/questions/3501382/checking-whether-a-variable-is-an-integer-or-not) — hostingutilities.com, Mar 17 '18 at 05:31
well, i know i can use String.isNumeric, but my biggest problem is including this without my code getting huge, for what seems like a simple problem — YSquared Yobozo, Mar 17 '18 at 05:34
You probably also want those values to be in a *certain* range? — Jus, Mar 17 '18 at 05:36
Yes, within 0 to 255, just edited the original post to clarify — YSquared Yobozo, Mar 17 '18 at 05:39

score 2 · Answer 1 · answered Mar 17 '18 at 05:33

2

Regex should help.

import re
s = "123,245,230"

if re.match("^\d{3},\d{3},\d{3}$", s):
    #process

answered Mar 17 '18 at 05:33

Rakesh

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the only problem with this is it requires the number be 3 digits long, so inputs like 2 have to be written as 002, unless there is a way around that? – YSquared Yobozo Mar 17 '18 at 05:44
You can then use \d{2,3} – Rakesh Mar 17 '18 at 06:28
is there a way to specify the number value being between 0 and 255 with regex in this manner? – YSquared Yobozo Mar 18 '18 at 02:56

score 0 · Answer 2 · answered Mar 17 '18 at 05:39

0

Im not clear on whatg you're trying to do with the while loop.

Also you could check that the value is a valid rgb value as per below:

colorListString = '123,245,230'
colorMatrix = []
colorList =colorListString.split(",")
if len(colorList)==3:
    for i in range(3):
        val = int(colorList[i])
        if val <= 255 and val >= 0: 
            colorList[i] = val
    colorMatrix +=[colorList]
    print(colorMatrix)

answered Mar 17 '18 at 05:39

proximacentauri

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the While loop was just me saying that "if its not a proper input, ask again" – YSquared Yobozo Mar 17 '18 at 05:40

score 0 · Accepted Answer · answered Mar 17 '18 at 05:55

If you're trying to force an exception to be thrown if they enter more then 3 numbers, there are a few ways to do it:

>>> colorListString = '255, 255, 255, 255'
>>> # Unpacking
>>> r, g, b = colorListString.split(",")
ValueError: too many values to unpack (expected 3)
>>> # maxsplit argument to split
>>> colorList = colorListString.split(",", 2)
>>> for i in range(3): colorList[i]=int(colorList[i])
ValueError: invalid literal for int() with base 10: ' 255, 255'
>>> # Just check it manually
>>> colorList = colorListString.split(",")
>>> if len(colorList != 3) raise ValueError('RGB please')
ValueError: RGB please

No need to get any fancier, like counting the commas before the split or using a regex.

well, i didnt necessarily want an exception, i just want it to repeat the input, error message would just be a bonus, but not required — YSquared Yobozo, Mar 17 '18 at 06:06
@YSquaredYobozo Well then, you can change the last one to do anything you want after the `if`, and the others, you can wrap in `try`/`except` to handle the exception. — abarnert, Mar 17 '18 at 06:08

Austin · Answer 4 · 2018-03-18T04:25:36.553

0

Simple 1-liner without regex:

s = "123,245,230"
if all(x <= 3 for x in [len(i) if int(i) >= 0 and int(i) <= 255 else 4 for i in s.split(',')]):
    # process

This works with strings like 2,123,220. You don't require to use 002,123,220.

Also takes care that the 3-digit number in the string separated by comma is between 0 and 255.

edited Mar 18 '18 at 04:25

answered Mar 17 '18 at 06:20

Austin

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but this doesnt specify that the input has to be between 0 and 255 – YSquared Yobozo Mar 18 '18 at 02:54
Aww, missed that one. I've updated my answer. It's a quick trick but works. – Austin Mar 18 '18 at 04:26

How to test a string as a list of integers Python

4 Answers4