Grouping similar substrings in list

group_substrings.py

from itertools import groupby

test_list = ['geek_1', 'coder_2', 'geek_4', 'coder_3', 'pro_3']

test_list.sort()

res = [list(i) for j, i in groupby(test_list,
                  lambda a: a.split('_')[0])]

#The original list is : [‘coder_2’, ‘coder_3’, ‘geek_1’, ‘geek_4’, ‘pro_3’]
#The grouped list is : [[‘coder_2’, ‘coder_3’], [‘geek_1’, ‘geek_4’], [‘pro_3’]]