It's hard to say, but looking at your code I'm guessing you are failing at the test case where n=0 which will lead to your tmp list being empty regardless of how you change indices.

In general, to troubleshoot you should first try printing the test inputs - in Python just add:

def zeros(n):
  print(n)
  rest of your code here

where here n is the name of the input, to your code so that you can see in the console which inputs are causing you to fail.