finding if a string doesn't have any integers

Question

I have the code:

user_input = input('>>>: ')
if not re.search('[0-9]', user_input):
    print('That wasn\'t an integer.')
else:
    print('That was an integer!')
    print(user_input)

It basically tries to determine if the user's input is (mathematically) an integer or not. This works if the input is 'adgx'; the code recognizes that these aren't within the range 0-9, and print's 'That wasn't an integer.'. I need the program to print 'That wasn't an integer.' if the input is for example 'a3h1d', but it doesn't. I assume because the input technically contained numbers that were within the range, it satisfied the statement. I need it so that if the input is 'a3h1d' that the program prints 'That wasn't an integer.'.

This question already has an answer here: http://stackoverflow.com/questions/5424716/how-to-check-if-string-input-is-a-number — Thierry Lathuille, Apr 12 '17 at 16:35
If you want to accept negative numbers, use `int(user_input)` and catch the error. If only positive integers, use `user_input.isdigit()` — dawg, Apr 12 '17 at 16:40

score 1 · Answer 1 · answered Apr 12 '17 at 16:33

1

If you aren't tied to the idea of using a regex for this, I would suggest simply using str.isdigit

user_input = input('>>>: ')
if not user_input.isdigit():
    print('That wasn\'t an integer.')
else:
    print('That was an integer!')

There's also this approach

try:
    user_input = int(input('>>>: '))
    print('That was an integer!')
except ValueError:
    print('That wasn\'t an integer.')

answered Apr 12 '17 at 16:33

Cory Kramer

114,268
16
167
218

I can't use try, because though i know i didn't include it but i have now after editing, because then it will convert '00000000' to '0' when i need to print it – Anya Apr 12 '17 at 16:40

Haroldo_OK · Accepted Answer · 2017-04-12T19:45:04.670

0

You can also use re.match() plus the beginning-of-string and end-of-string markers:

user_input = input('>>>: ')
if not re.match('^[0-9]+$', user_input):
    print('That wasn\'t an integer.')
else:
    print('That was an integer!')

Remember that, in regex:

^ Matches the start of a line;
$ Matches the end of a line;
+ Indicates that the previous pattern should appear one or more times.

I would recommend taking a look at Python official 're' documentation for a more complete and well explained list.

edited Apr 12 '17 at 19:45

answered Apr 12 '17 at 16:36

Haroldo_OK

6,612
3
43
80

1

Should be `r'^[0-9]+$'`, otherwise it only matches a single digit. – jonrsharpe Apr 12 '17 at 16:38
Very true; I missed that detail. :P – Haroldo_OK Apr 12 '17 at 16:40
Could you explain the metacharacters and what they're doing? I'm still learning regex – Anya Apr 12 '17 at 17:15
Okay, added a brief explanation. – Haroldo_OK Apr 12 '17 at 19:45

finding if a string doesn't have any integers

2 Answers2