`input()` returns a string, not a list.  For input '1010' you're effectively computing this:

>>> int('1' * 8) + int('1' * 2) # = 11111111 + 11
11111122

which is the correct answer.  If you want your input to be a list of integers instead of a string, try, e.g.,

a = input("please enter a binary integer ")
a = list(map(int, a))