我计算最大二进制间隙的函数不起作用，但我不知道为什么

Question

I'm working through the Codility problems and I have gotten the first one almost correct. The task is to write a function which returns the longest binary gap (a sequence of 0s in between 1s) in a binary number. I have gotten all of the test numbers correct apart from 9, which should be 2 (its binary representation is 1001) but which my function returns as 0. I can't seem to figure out why.

My function is as follows:

def Solution(N):
  x = bin(N)[2:]
  x_string = str(x)
  y = (len(x_string))
  count = 0
  max = 0
  for index, item in enumerate(x_string):
      if item == "1":
          count = 0
      elif item == "0" and x_string[index + 1:y-1] != "0"*(y -1 - (index + 1)):
          count = count + 1
          if count > max:
              max = count
  print(max)

The complicated indexing and second condition in the elif statement is so that when a 0 is not contained between two 1s then it isn't recognised as the beginning of a binary gap eg when the for loop looks at the second character in bin(16) = 10000, it doesn't set count to 1 because all of the remaining characters in the string are also zero.

Answer 1

Simple solution

x_string[index + 1:y-1] != "0"

this bit wants to take a look at the whole string that's left, but the end argument isn't inclusive,it's exluded, so if string length = 4; string[0:4] is the whole string.

source: https://docs.python.org/3/tutorial/introduction.html

-Sam