This will work
all = [a1, b1, b2, a2,.....]
map(lambda x: x.start(),all)
simple example
all = ["MILK","BREAD","EGGS"]
map(lambda x:x.lower(),all)
>>>['milk','bread','eggs']
and in python3
all = ["MILK","BREAD","EGGS"]
list(map(lambda x:x.lower(),all))
>>>['milk','bread','eggs']