TheAlgorithms/Python · error · IndexError

Warning: Tree is empty! please use another.

Error message

Warning: Tree is empty! please use another.

What it means

Raised by BinarySearchTree.search() in data_structures/binary_tree/binary_search_tree.py when the tree is empty (self.empty() is True, i.e. no root). Searching requires at least one node to start the descent, so the method raises IndexError with a 'Warning:' message instead of returning None. Note the unusual choice of IndexError for this condition.

Source

Thrown at data_structures/binary_tree/binary_search_tree.py:226

        {'30': (None, {'40': (None, 50)})}
        >>> tree.search(40)
        {'40': (None, 50)}
        >>> tree.search(50)
        50
        >>> tree.search(5) is None  # element not present
        True
        >>> tree.search(0) is None  # element not present
        True
        >>> tree.search(-5) is None  # element not present
        True
        >>> BinarySearchTree().search(10)
        Traceback (most recent call last):
            ...
        IndexError: Warning: Tree is empty! please use another.
        """

        if self.empty():
            raise IndexError("Warning: Tree is empty! please use another.")
        else:
            node = self.root
            # use lazy evaluation here to avoid NoneType Attribute error
            while node is not None and node.value is not value:
                node = node.left if value < node.value else node.right
            return node

    def get_max(self, node: Node | None = None) -> Node | None:
        """
        We go deep on the right branch

        >>> BinarySearchTree().insert(10, 20, 30, 40, 50).get_max()
        50
        >>> BinarySearchTree().insert(-5, -1, 0.1, -0.3, -4.5).get_max()
        {'0.1': (-0.3, None)}
        >>> BinarySearchTree().insert(1, 78.3, 30, 74.0, 1).get_max()
        {'78.3': ({'30': (1, 74.0)}, None)}
        >>> BinarySearchTree().insert(1, 783, 30, 740, 1).get_max()

View on GitHub (pinned to f5988cc097)

Solutions

1. Check emptiness before searching: if tree.empty(): return None / handle.
2. Ensure inserts complete before any search runs (ordering in setup code).
3. Catch IndexError if you must, but prefer the explicit empty() guard — the exception type is unconventional.

Example fix

# before
node = BinarySearchTree().search(10)  # IndexError

# after
tree = BinarySearchTree()
node = None if tree.empty() else tree.search(10)

node = tree.search(value) if not tree.empty() else None

try:
    node = tree.search(value)
except IndexError:
    node = None  # empty tree, nothing to find

When it happens

Trigger: Calling BinarySearchTree().search(10) on a freshly constructed tree, or searching a tree after all nodes were removed (remove() can leave an empty tree).

Common situations: Searching before any inserts (data not yet loaded), removing all elements and then querying, or test code that instantiates a tree and immediately probes it.

Related errors

• Value {value} not found
• The parameter s must not be empty.
• The parameter bwt_string must not be empty.
• We need some text to work with.
• The array is empty.

AI-assisted analysis of TheAlgorithms/Python@f5988cc097 (2026-08-14). Data as JSON: /api/errors/d7b4bc68fe788d1e. Report an issue: GitHub.