Python Regex not capturing single strings

Question

bigger_list_of_names = ['Jim', 'Bob', 'Fred', 'Cam', 'Reagan','Alejandro','Dee','Rana','Denisha','Nicolasa','Annett','Catrina','Louvenia','Emmanuel','Dina','Jasmine','Shirl','Jene','Leona','Lise','Dodie','Kanesha','Carmela','Yuette',]
name_list = ['Jim', 'Bob', 'Fred', 'Cam']
search_people = re.compile(r'\b({})\b'.format(r'|'.join(name_list)), re.IGNORECASE)
print(search_people)

for names in bigger_list_of_names:
    found_them = search_people.search(names, re.IGNORECASE | re.X)
    print(names)
    if found_them:
        print('I found this person: {}'.format(found_them.group()))
    else:
        print('Did not find them')

The issue I am having is the regex does not find the names at all and keeps hitting the else: I have tried re.search, re.findall, re.find, re.match, re.fullmatch, etc. They all return None. The only way for it to find anything is if I use re.finditer but that would not allow me to use .group().

The output of the re.compile is re.compile('\\b(Jim|Bob|Fred|Cam)\\b', re.IGNORECASE)

I tested it on https://regex101.com/ () and it looks like its working but not in the python.

Here is my console output:

Am I missing anything?

Try removing the flags from your `search_people.search` call — Iain Shelvington, Mar 31 '20 at 23:11

score 3 · Answer 1 · answered Mar 31 '20 at 23:26

The second argument to a compiled regular expression is the position in the string to start searching, not flags to use with the regex (the third, also optional argument, is the ending position to search). See the docs for Regular expression objects for details.
If you want to specify a case-insensitive search, pass re.IGNORECASE to re.compile. For this regex, re.X isn't needed.

score 1 · Accepted Answer · answered Mar 31 '20 at 23:52

I'm a little late but I had the same issue before. It looks like you are using pycharm, if you check the auto complete thing (if you don't have it turned off) it would say:

pattern.search(self, string, pos, endpos)

Instead of adding flags in the .search() part, you will need to add the flags in the re.compile part. Since re.compile() actually accepts the flags.

What it looks like in pycharm auto complete:

re.compile(pattern, flags)

So it would look a bit like this:

search_people = re.compile(r'\b({})\b'.format(r'|'.join(name_list)), re.IGNORECASE | re.X)

for names in bigger_list_of_names:
    found_them = search_people.search(names)
    print(names)
    if found_them:
        print('I found this person: {}'.format(found_them.group()))
    else:
        print('Did not find them')

CypherX · Answer 3 · 2020-04-01T06:15:39.193

0

What you are trying to do, does not require a regex search. You can achieve the same as follows.

search_result = []
targets = set(names_list)
for name in set(bigger_list_of_names):
    if name in targets:
        search_result.append(name)
        print(f'Found name: {name}')
    else:
        print(f'Did not find name: {name}')
print(search_result)

Shorter version using list-comprehension

search_result = [name for name in set(bigger_list_of_names) if name in targets]

edited Apr 01 '20 at 06:15

answered Mar 31 '20 at 23:29

CypherX

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1

Case insensitive searching is probably better done with a regex. For case sensitive matching, your code would work, but then I'd suggest using a set for faster lookup. If the set of names to look for is called `targets`, then `matches = [ name for name in bigger_list_of_names if name in targets ]` is pretty good. – cco Apr 01 '20 at 00:00
Hey thank you trying to help out. The lists are just a placeholder for something a little more complicated but works the same way. It was easier to explain the problem like this. – unDucked Apr 01 '20 at 00:17
@cco made changes, as you suggested. – CypherX Apr 01 '20 at 06:16
Cool. Note that there is no need to make `bigger_list_of_names` a set; you're just iterating it, no looking up. Making it a set doesn't cost much, but it doesn't help at all. The big win is with `targets = set(names_list)`, because that changes the lookups from O(n) to O(1). – cco Apr 01 '20 at 21:06

Python Regex not capturing single strings

3 Answers3