python re: search and findall give different results

Question

why do search and findall give different results?

result = re.search(r'Bat(wo)?man', 'The Adventures of Batman')

print(result) # found

re.findall(r'Bat(wo)?man', 'The Adventures of Batman') # empty list

Answer 1

When I run this, I don't get an empty list, but a list containing a single empty string: [''].

From the docs (emphasis mine):

The result depends on the number of capturing groups in the pattern. If there are no groups, return a list of strings matching the whole pattern. If there is exactly one group, return a list of strings matching that group. If multiple groups are present, return a list of tuples of strings matching the groups. Non-capturing groups do not affect the form of the result.

You use a capturing group ((wo)?), so the results only contain the part of the string that matched that group.

You can fix this by changing the group to a non-capturing group:

>>> print(re.findall(r'Bat(?:wo)?man', 'The Adventures of Batman'))
['Batman']