You're modifying the list you're iterating over. If you do that, the size of the list shrinks, so eventually lst[i] will point beyond the list's boundaries.
>>> lst = [1,2,3]
>>> lst[2]
3
>>> lst.remove(1)
>>> lst[1]
3
>>> lst[2]
Traceback (most recent call last):
File "", line 1, in
IndexError: list index out of range
It's safer to construct a new list:
return [item for item in lst if item[0]!=1 and item[1]!=1]
