geekcomputers/Python · error · Exception

Invalid Position

Error message

Invalid Position

What it means

remove_at in the doubly linked list raises a generic Exception when idx < 0 or idx >= len() (the code writes self.len() <= idx). Indices 0 and length-1 delegate to pop_front/pop_back after validation; everything else unlinks the node in place.

Source

Thrown at LinkedLists all Types/doubly_linked_list.py:95

                break
            print(f"{temp.data} <=>", end=" ")
            temp = temp.next
        print("NULL")

    def len(self):
        return self.length  # O(1) length calculation
        # if self.head is None:
        #     return 0
        # count = 0
        # temp = self.head
        # while temp:
        #     count += 1
        #     temp = temp.next
        # return count

    def remove_at(self, idx):
        if idx < 0 or self.len() <= idx:
            raise Exception("Invalid Position")
        if idx == 0:
            self.pop_front()
            return
        elif idx == self.length - 1:
            self.pop_back()
            return
        temp = self.head
        dist = 0
        while dist != idx - 1:
            dist += 1
            temp = temp.next
        temp.next = temp.next.next
        temp.next.prev = temp.next.prev.prev
        self.length -= 1

    def insert_at(self, idx: int, data):
        if idx < 0 or self.len() < idx:
            raise Exception("Invalid Position")

View on GitHub (pinned to 40f4cd2652)

Solutions

1. Check 0 <= idx < dll.len() before calling remove_at
2. Handle 'not found' (-1) results separately instead of passing them to remove_at
3. In removal loops, account for the list shrinking each iteration

Example fix

# before
dll.remove_at(idx)
# after
if 0 <= idx < dll.len():
    dll.remove_at(idx)
else:
    raise IndexError('remove_at index out of range')

def can_remove(dll, idx) -> bool:
    return 0 <= idx < dll.len()

try:
    dll.remove_at(idx)
except Exception:
    raise IndexError(f'remove index {idx} out of range') from None

When it happens

Trigger: Calling remove_at(idx) with a negative index, an index equal to the list length, or on an empty list; using a stale index after the list shrank between lookup and removal.

Common situations: Index computed from find returning -1 on miss; concurrent modification patterns where the list changed between measuring and removing; 1-based vs 0-based confusion after porting pseudocode.

Related errors

• Invalid Position
• Invalid Position

AI-assisted analysis of geekcomputers/Python@40f4cd2652 (2026-08-27). Data as JSON: /api/errors/ac70e8c50a1615ff. Report an issue: GitHub.