Something like this,look into findall off re module.
Dont use str as variable,it`s a builtin key word.
Help on class str in module __builtin__:
>>> import re
Help on function findall in module re:
findall(pattern, string, flags=0)
Return a list of all non-overlapping matches in the string.
If one or more groups are present in the pattern, return a
list of groups; this will be a list of tuples if the pattern
has more than one group.
Empty matches are included in the result.
text = '''\
Subs cars are test driving in space,and many pigs are flying.
test_match = re.findall(r'\w+[s]\b', text)
#->['Subs', 'cars', 'pigs']