Question

A regex answers a yes or no question – does the string match the pattern.

I want to separate the no’s into two categories:

• invalid strings that are prefixes of valid strings
• invalid strings that are not prefixes of valid

Here’s an example (regular expression 01+2):

• 012 is valid

• 12 is invalid; it is not a prefix of a valid string

• 01 is invalid; it is a prefix of a valid string: 012

Java can do this.

Can re do this? If not, is there a library that can make this distinction?

Answer 1

I second the recommendation of regex. The module is simply fantastic.

Here’s an example of fuzzy matching with regex:

import regex

# traditional matching - three digits
r = '(?:\d\d\d)'
print regex.findall(r, '1xx22yy333zz')
## ['333']

# fuzzy matching - three digits, allow at most 2 deletions
r = '(?:\d\d\d){d<3}'
print regex.findall(r, '1xx22yy333zz')
## ['1', '22', '333']

The {d<3} part basically says “if we add one or two chars to that, that would be a match” – the same as point 3. in your question.

See http://pypi.python.org/pypi/regex for more info (look for ‘Approximate “fuzzy” matching’).