In [1]: L=[1,2,3,4,5,6,0,0,0,0,0,0,1,2,3,4,5,6]

In [2]: pop=0

In [3]: for i in L:
   ...:     if i != 0:
   ...:         pop += 1
   ...:     elif i == 0:
   ...:         L.pop(pop)
   ...:
Out[3]: 0
Out[3]: 0
Out[3]: 0

In [4]: L
Out[4]: [1, 2, 3, 4, 5, 6, 0, 0, 0, 1, 2, 3, 4, 5, 6]

In [5]: