As stated in Cory Kramer's answer, simply remove the line binary = [] at the beginning of your code and it will work perfectly.

Here is an alternative algorithm, given as food for thought:

def binatointeger(binary):
  number = 0
  for b in binary:
    number = (2 * number) + b
  return number

Important note

Note that the resulting number is not in decimal. It's a python integer. Internally in the computer, python integers are stored in binary. The conversion to decimal representation, i.e., to a string of digits, happens when calling the function print, str, or repr, to print the number to screen.