How to Link Parent and Child Span Elements in Python

This code defines a lightweight mock element class and a function that links child elements to a parent when their ranges are nested within the parent's range.

Easy Python 3.9+ Aug 9, 2026 Observability & SRE 14 views 0 copies

spans nesting mock hierarchy

Python code

33 lines

Python 3.9+

class MockElement:
    def __init__(self, name, start, end, children=None):
        self.name = name
        self.start = start
        self.end = end
        self.children = children or []

    def __repr__(self):
        return f"MockElement({self.name}, {self.start}-{self.end})"


def link_parent_child(parent, child):
    """Link a child element to its parent if spans overlap or are nested."""
    if child.start >= parent.start and child.end <= parent.end:
        parent.children.append(child)
        return True
    return False


if __name__ == "__main__":
    parent = MockElement("div", 0, 10)
    child1 = MockElement("p", 2, 5)
    child2 = MockElement("span", 6, 8)
    child3 = MockElement("h1", -1, 3)  # invalid overlap

    results = {
        "child1_linked": link_parent_child(parent, child1),
        "child2_linked": link_parent_child(parent, child2),
        "child3_linked": link_parent_child(parent, child3),
    }

    print("Link results:", results)
    print("Parent children:", parent.children)

Output

stdout

Link results: {'child1_linked': True, 'child2_linked': True, 'child3_linked': False}
Parent children: [MockElement(p, 2-5), MockElement(span, 6-8)]

How it works

The MockElement class stores a name and start/end positions to represent a span. The link_parent_child function checks if the child's span is fully contained within the parent's span using start and end comparisons. If the condition holds, the child is appended to the parent's children list and True is returned; otherwise False. This provides a simple containment check useful for building hierarchical structures from flat span data. The example demonstrates correct linking for nested spans and rejects an out-of-range child.

Common mistakes

Using half-open intervals inconsistently (assuming start is inclusive but end exclusive) without defining it clearly.
Not considering overlapping but non-nested spans that should be siblings, not parent-child.
Forgetting that this function mutates the parent's children list, which may have side effects in larger code.

Variations

Use a dataclass with slots for better performance when handling many elements.
Implement a function that returns a new tree instead of mutating the parent in place.

Real-world use cases

Building nested HTML element trees from flat parsed markup where each tag has offsets.
Validating that child components' layout ranges fit within parent containers in UI testing mocks.
Organizing log spans into parent-child relationships for trace or span visualization.

How to Link Parent and Child Span Elements in Python

Python code

Output

How it works

Common mistakes

Variations

Real-world use cases

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