import re
my_list = ['1 ab ac bbba','23 abcba a aabb ab','345 ccc ab aaaaa']
my_list2 = []
for str in my_list:
my_list2.append(re.sub("[^abc]", "", str))
print(my_list2)
aW1wb3J0IHJlCgpteV9saXN0ID0gWycxIGFiIGFjIGJiYmEnLCcyMyBhYmNiYSBhIGFhYmIgYWInLCczNDUgY2NjIGFiIGFhYWFhJ10KbXlfbGlzdDIgPSBbXQpmb3Igc3RyIGluIG15X2xpc3Q6CiAgICBteV9saXN0Mi5hcHBlbmQocmUuc3ViKCJbXmFiY10iLCAiIiwgc3RyKSkKCnByaW50KG15X2xpc3QyKQ==