querystree.py

def querytree(s):
    """
    Build a list of nodes to describe the nested structure of a querystring.

    """
    Node = namedtuple("Node", "level value")
    stack = []
    # A node has children if there is a left paren before a right paren,
    # starting from hte index position where the node begins.
    for idx, char in enumerate(s):
        if char == "(":
            stack.append(idx)
            if len(stack) > 1:
                start = stack[-2]
                substr = s[start+1:idx]
                yield Node(len(stack)-1, substr)
        elif char == ")":
            start = stack.pop()
            substr = s[start+1:idx]
            yield Node(len(stack), substr)