Check Python String Formatting

Question

I can accept user's input in two formats:

123
123,234,6028

I need to write a function/a few lines of code that check whether the input follows the correct format.

The rules:

If a single number input, then it should be just a number between 1 and 5 digits long
If more then one number, then it should be comma-separated values, but without spaces and letters and no comma/period/letter allowed after the last number.

The function just checks if formatting correct, else it prints Incorrect formatting, try entering again.

I would assume I would need to use re module.

Thanks in advance

You could do it with re, but its simple enough that a more brute force solution with str.split, among other options. Its not going to be a big deal either way. If you like re, try an implementation and come back if you need specific help. — tdelaney
– tdelaney, Commented May 8, 2022 at 20:28
I have a doubt regarding your comment on "no dots" after the last number. Do you want to allow floats? How? — mozway
– mozway, Commented May 8, 2022 at 20:47
@mozway I would not want floats. Simply numbers (in my case they are IDs) separated by commas (if it's more than 1 number). Thank you for you answer. Could you do a minor correct so that input can be only from 1 to 5 digits long? — Aleksei
– Aleksei, Commented May 8, 2022 at 21:00
@Alex thanks for the feedback, I updated the answer to only allow numbers of 1 to 5 digits — mozway
– mozway, Commented May 9, 2022 at 4:51

mozway · Accepted Answer · 2022-05-09 04:50:18Z

2

You can use a simple regex:

import re

validate = re.compile('\d{1,5}(?:,\d{1,5})*')

validate.fullmatch('123') # valid

validate.fullmatch('123,456,789') # valid

validate.fullmatch('1234567') # invalid

Use in a test:

if validate.fullmatch(your_string):
    # do stuff
else:
    print('Incorrect formatting, try entering again')

edited May 9, 2022 at 4:50

answered May 8, 2022 at 20:38

mozway

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2 Comments

DarrylG Over a year ago

validate.fullmatch('1234567') matches, but shouldn't by rule 1.

mozway Over a year ago

@DarrylG I had misread, I updated

Matt Pitkin · Accepted Answer · 2022-05-08 21:16:21Z

1

Another option is:

def validString(string):
    listofints = [v.isdigit() for v in string.split(",") if 0 < len(v) < 6]
    if not len(listofints) or not all(listofints):
        print("Incorrect formatting, try entering again.")

edited May 8, 2022 at 21:16

answered May 8, 2022 at 20:43

Matt Pitkin

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1 Comment

DarrylG Over a year ago

validString('1234567') should detect incorrect formatting, but doesn't.

Schnitte · Accepted Answer · 2022-05-08 20:36:49Z

0

The following code should leave the Boolean variable valid as True if the entered ibnput complies with your rules and False otherwise:

n = input("Your input: ")
valid = True
try:
    if int(n) > 9999: 
        valid = False
except:
    for character in n:
        if not character in "0123456789,":
            valid = False
    if n[-1] == ",":
        valid = False

answered May 8, 2022 at 20:36

Schnitte

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1 Comment

DarrylG Over a year ago

For ,,0 valid is True but should be False.

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