Traverse SCons node graph

import SCons

def has_build_targets():
    return len(SCons.Script.BUILD_TARGETS) > 0

def get_start_nodes():
    if has_build_targets():
        return SCons.Script.Alias(SCons.Script.BUILD_TARGETS)
    return [SCons.Script.Dir('.')]

def walk(node):
    print "walk", str(node)
    children = node.children()
    for child in children:
        if child.has_builder():
            environ = child.get_build_env()
            bn = child.get_builder().get_name(environ)
            print "discovered %s (%s)" % (str(child), bn)
        walk(child)


for node in get_start_nodes():
    if str(node) in ['/']:
        continue
    walk(node)