Python Removing last character _ from string using regex -

i know there bunch of other regex questions, hoping point out wrong regex. have done research , looks should work. used rubular test it, yes know regex ruby, same rules used should apply python looks in python docs

currently have

a = ["sdfsd_sfsdf234234","sdfsdf_sdfsdf_234324","tsfsd_sdf_213123"] c = [re.sub(r'[a-z]+', "", x) x in a] 

which returns

['sdfsd_sfsdf', 'sdfsdf_sdfsdf_', 'tsfsd_sdf_'] 

but want return

['sdfsd_sfsdf', 'sdfsdf_sdfsdf', 'tsfsd_sdf'] 

i try use regex

c = [re.sub(r'$?_[^a-z_]+', "", x) x in a] 

but getting error

traceback (most recent call last):   file "<stdin>", line 1, in <module>   file "/usr/lib64/python2.6/re.py", line 151, in sub     return _compile(pattern, 0).sub(repl, string, count)   file "/usr/lib64/python2.6/re.py", line 245, in _compile     raise error, v # invalid expression 

can me figure out doing wrong?

the error in:

c = [re.sub(r'$?_[^a-z_]+', "", x) x in a] 

is caused ?, not preceded characters doesn't know match 0 or 1 times. if change to:

>>> [re.sub(r'_?[^a-z_]+$', "", x) x in a] ['sdfsd_sfsdf', 'sdfsdf_sdfsdf', 'tsfsd_sdf'] 

it works expect.

another thing, $ used detonate end of line, shouldn't first character.