TheAlgorithms/Python · error · TypeError

Value must be an integer.

Error message

Value must be an integer.

What it means

Raised by TreeNode.__post_init__ (dataclasses/serialize_deserialize_binary_tree.py) when the value field is not an int. The dataclass validates its value immediately after construction, so TreeNode('1'), TreeNode(1.0), or TreeNode(None) all fail with TypeError. Note bool is an int subclass and passes; the check is isinstance(self.value, int), so True/False are accepted.

Source

Thrown at data_structures/binary_tree/serialize_deserialize_binary_tree.py:24

@dataclass
class TreeNode:
    """
    A binary tree node has a value, left child, and right child.

    Props:
        value: The value of the node.
        left: The left child of the node.
        right: The right child of the node.
    """

    value: int = 0
    left: TreeNode | None = None
    right: TreeNode | None = None

    def __post_init__(self):
        if not isinstance(self.value, int):
            raise TypeError("Value must be an integer.")

    def __iter__(self) -> Iterator[TreeNode]:
        """
        Iterate through the tree in preorder.

        Returns:
            An iterator of the tree nodes.

        >>> list(TreeNode(1))
        [1,null,null]
        >>> tuple(TreeNode(1, TreeNode(2), TreeNode(3)))
        (1,2,null,null,3,null,null, 2,null,null, 3,null,null)
        """
        yield self
        yield from self.left or ()
        yield from self.right or ()

    def __len__(self) -> int:

View on GitHub (pinned to f5988cc097)

Solutions

1. Convert before constructing: TreeNode(int(raw)) for string input
2. Sanitize at the parse boundary: `int(value.strip())` right after reading tokens
3. If non-int payloads are legitimate, copy the dataclass and widen the field type instead of fighting the guard

Example fix

# before
node = TreeNode('5')  # TypeError

# after
node = TreeNode(int('5'))

from data_structures.binary_tree.serialize_deserialize_binary_tree import TreeNode

node = TreeNode(value) if isinstance(value, int) and not isinstance(value, bool) else TreeNode(int(value))

def is_int_value(v: object) -> bool:
    """True for real ints (excluding bool, which the dataclass accepts)."""
    return isinstance(v, int)

try:
    node = TreeNode(raw)
except TypeError:
    node = TreeNode(int(raw))  # coerce string/float payloads

When it happens

Trigger: TreeNode('5') with a string (typical when building nodes from unparsed text/JSON); TreeNode(1.5) from float math; TreeNode(None) as a 'missing' marker; passing a numpy int64 (isinstance check may pass since it subclasses int in some builds, but plain object dtype values will fail).

Common situations: Deserializing JSON where numbers arrive as strings; reading node values from CSV/text without int() conversion; mixing float coordinates into a tree meant for integer labels.

Related errors

• operation can not be conducted on an object of type {type(nu
• Input value must be an 'int' type
• plaintext must be a string
• key must be a string
• ciphertext must be a string

AI-assisted analysis of TheAlgorithms/Python@f5988cc097 (2026-08-14). Data as JSON: /api/errors/c3c8d1e8a18768b2. Report an issue: GitHub.