TheAlgorithms/Python · error · Exception

Empty heap

Error message

Empty heap

What it means

Raised by Heap.pop() (heap/heap.py) when heap_size == 0: the if/elif chain handles sizes >= 2 and == 1, and the else raises generic Exception('Empty heap'). Popping from an empty max heap has no element to return. Note this is a bare Exception, not IndexError/ValueError, so `except IndexError` will NOT catch it — a known wart of this implementation.

Source

Thrown at data_structures/heap/heap.py:194

        >>> h.extract_max()
        514

        >>> h = Heap()
        >>> h.build_max_heap([1,2,3,4,5,6,7,8,9,0])
        >>> h.extract_max()
        9
        """
        if self.heap_size >= 2:
            me = self.h[0]
            self.h[0] = self.h.pop(-1)
            self.heap_size -= 1
            self.max_heapify(0)
            return me
        elif self.heap_size == 1:
            self.heap_size -= 1
            return self.h.pop(-1)
        else:
            raise Exception("Empty heap")

    def insert(self, value: T) -> None:
        """
        insert a new value into the max heap

        >>> h = Heap()
        >>> h.insert(10)
        >>> h
        [10]

        >>> h = Heap()
        >>> h.insert(10)
        >>> h.insert(10)
        >>> h
        [10, 10]

        >>> h = Heap()
        >>> h.insert(10)

View on GitHub (pinned to f5988cc097)

Solutions

1. Guard with emptiness check before popping: `while h.heap_size > 0: h.pop()`
2. Catch the generic exception: `except Exception` — but prefer the guard, since the class is bare Exception (matches nothing narrower)
3. Pop at most len elements: iterate `for _ in range(h.heap_size)`

Example fix

# before
while True:
    top = h.pop()  # eventually Exception('Empty heap')

# after
while h.heap_size > 0:
    top = h.pop()

while h.heap_size > 0:
    top = h.pop()

try:
    top = h.pop()
except Exception as e:  # NOTE: bare Exception — not IndexError/ValueError
    if str(e) != 'Empty heap':
        raise
    top = None

When it happens

Trigger: h.pop() on a fresh Heap(); popping more times than elements inserted (e.g. drain loop that pops n+1 times); popping after exceptions interrupted inserts.

Common situations: Drain loops like `while True: h.pop()`; top-N extraction where the requested N exceeds heap size; reusing a heap object across test cases without re-initialization.

Related errors

• Can't get top element for the empty heap.
• Can't get top element for the empty heap.
• Binary search tree is empty
• binary tree cannot be empty
• remove_first from empty list

AI-assisted analysis of TheAlgorithms/Python@f5988cc097 (2026-08-14). Data as JSON: /api/errors/ad9a8a95384b69db. Report an issue: GitHub.