In Python, how do I restart a for loop within a while loop? The furthest out loop is a while loop that runs while r < y(length of integer list)

Question

The integer list is essentially a random integer list of mostly integers in an excel file but there are some blocks of zeroes I want to identify. Ex. [3,3,3,0,0,4,0,6,0,0,7]. I just want to run through the list so that I can print: first block of zeroes start at index 3 and end at index 4, second block etc.

The list is a single column in excel, and spans thousands of rows.

The way I am doing that is with the following code:

r = 1
while r+1000 < y:
   for q in range(r,y-1):
      if sheet.cell_value(q,3) == '0':
          start = q
          print(str(start))
          for e in range(q,y-1):
              if sheet.cell_value(e,3) != 0:
                  r = e
                  print(str(end))
                  break
          break

The prints are there so I can check if it is going right. But what's happening now in the output is it never stops and only prints the start value.

Answer 1

You could do something similar to this to get a listing of where every group of 0's start and end.

>>> li = [3,3,3,0,0,4,0,6,0,0,7]
>>> tracking_zeros = False
>>>
>>> for i, n in enumerate(li):
...     if n == 0:
...         if not tracking_zeros:
...             print(f"start zeros: {i}")
...             tracking_zeros = True
...     else:
...         if tracking_zeros:
...             print(f"  end zeros: {i}")
...             tracking_zeros = False
...             
start zeros: 3
  end zeros: 5
start zeros: 6
  end zeros: 7
start zeros: 8
  end zeros: 10

Not counting single zeroes:

>>> tracking_zeros = False
>>>
>>> for i, n in enumerate(li):
...     if n == 0:
...         if not tracking_zeros and li[i+1] == 0:
...             print(f"start zeros: {i}")
...             tracking_zeros = True
...     else:
...         if tracking_zeros:
...             print(f"  end zeros: {i}")
...             tracking_zeros = False
...             
start zeros: 3
  end zeros: 5
start zeros: 8
  end zeros: 10

If the last item in the list is a 0, it'll throw an index error so you might need to account for that.

Could just append a non-zero value at the end before you do the loop to prevent that: li.append(1)