`Block.tree()` doesn't support depth limit

Start in dag/block.py at Block.tree() and the _walk_tree() helper, then inspect how the current depth-first paths are produced. Verify the existing unlimited behavior and the requested depth cases from the issue: depth 0 yields nothing, depth 1 yields top-level paths, and the default remains unlimited.

Block.tree() always traverses the entire tree. Go's Tree(path, depth) supports a depth parameter to limit traversal. This is useful for large DAGs where you only want to see the top-level structure.

Problem

In dag/block.py:

def tree(self) -> Iterator[str]:
    """Yield every path segment in this block's value (depth-first)."""
    yield from _walk_tree(self._value, "")

There's no way to limit the depth:

block = Block.encode(
    value={"a": {"b": {"c": "deep"}}},
    codec=dag_cbor.codec,
)

list(block.tree())  # → ["a", "a/b", "a/b/c"]
# No way to get just: ["a"]

Proposed Solution

Add an optional depth parameter:

def tree(self, depth: int = -1) -> Iterator[str]:
    """Yield every path segment in this block's value (depth-first).

    Parameters
    ----------
    depth:
        Maximum depth to traverse. -1 means unlimited (default).
        0 yields nothing. 1 yields only top-level keys.
    """
    if depth == 0:
        return
    yield from _walk_tree(self._value, "", max_depth=depth, current_depth=0)

Update _walk_tree():

def _walk_tree(node, prefix, max_depth=-1, current_depth=0):
    if max_depth >= 0 and current_depth >= max_depth:
        return
    if isinstance(node, dict):
        for k, v in node.items():
            child = f"{prefix}/{k}" if prefix else k
            yield child
            yield from _walk_tree(v, child, max_depth, current_depth + 1)
    elif isinstance(node, list):
        for i, v in enumerate(node):
            child = f"{prefix}/{i}" if prefix else str(i)
            yield child
            yield from _walk_tree(v, child, max_depth, current_depth + 1)

Related

• Go implementation: go-ipld-prime Node.Tree() method
• File: dag/block.py