dependency algorithm in python

def resolve_dependency(start,graph,li):
    if not graph[start]:
        pass
    else:
        for dep in graph[start]:
            resolve_dependency(dep,graph,li)
    if start not in li:
        li.append(start)
if __name__ == '__main__':
    graph = {'A':['D'],'B':['C'],'C':[],'D':['C']}
    start = 'D'
    li = []
    resolve_dependency(start,graph,li)
    li.pop()
    print li