Wrapper for recursive _detect_circle function

def detect_circle(nodes):
    """ Wrapper for recursive _detect_circle function """
    # Verify nodes and traveled types
    if not isinstance(nodes, dict):
        raise TypeError('"nodes" must be a dictionary')

    dependencies = set(nodes.keys())
    traveled = []

    heads = _detect_circle(nodes, dependencies, traveled)

    return DependencyTree(heads)