Here are different files and the output which should look like:

1. abc.csv - Correct
2. abc.csv.gz - Fail
3. abc.csv.csv - Fail
4. abc.def.csv - Correct

The present regex looks like .*[.]csv$ which passes cases 1 and 2, but not 3 and 4. I tried using {} and \B to allow only 1 extension but wasn't able to make it correctly.

CodePudding user response：

As said in the comments, filename.endswith('.csv') is in my opinion the most pythonic option.

That said, if you want to use a regex, you can use re.match('.*(?<!\.csv)(\.csv)$', s) or re.fullmatch('.*(?<!\.csv)(\.csv)', s)

s = 'abc.csv.csv'
re.match('.*(?<!\.csv)(\.csv)$', s)
# no match

s = 'abc.def.csv'
re.match('.*(?<!\.csv)(\.csv)$', s)
#<re.Match object; span=(0, 11), match='abc.def.csv'>

regex demo