clean some content inside tags

cl.py

import re
s = 'abcd<aaa>some thing <#^&*some more!#$@ </aaa> abcdefgasf <aaa>asfaf %^&*$saf  asf %$^ </aaa> <another tag> some text </another tag> <aaa>sfafaff#%%%^^</aaa>'
inside_tags = re.findall('<aaa>(.+?)</aaa>', s)
cleaned_contents = [ re.sub('\W', '_' ,content) for content in inside_tags ]

zipped = zip(inside_tags, cleaned_contents)
s
for old, new in zipped:
    s = s.replace(old, new)
print s