How do I check if input string is a valid regular expression or not in Python?

0 votes

HI all. Pretty simple question! 

Basically, in Java, I was able to use the following piece of code to check if my input string was a valid or an invalid regular expression. 

Check out the code:

boolean isRegex;
try {
  Pattern.compile(input);
  isRegex = true;
} catch (PatternSyntaxException e) {
  isRegex = false;
}

Now my question is that I want to know what the Python equivalent is of Pattern.compile() and PatternSyntaxException?

I am sure it exists in Python and that I am unaware of it. Using this in a project of mine.

All help appreciated!

Feb 12, 2019 in Python by Anirudh
• 2,080 points
4,640 views

1 answer to this question.

0 votes

Hi. Good question! Well, just like what we have in Java, for Python we have re.error exception just for this very purpose. Check out the code below to understand it better:

import re

try:
    re.compile('[')
    is_valid = True
except re.error:
    is_valid = False

What is re.error exception, you ask?

Here is the formal definition I got from the official documentation:

"Exception raised when a string passed to one of the functions here is not a valid regular expression or when some other error occurs during compilation or matching. "

Hope this helped! 

answered Feb 12, 2019 by Nymeria
• 3,520 points

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