[英]graph representation in Python with adjacency list
I have found the following Graph implementation in Python: 我在Python中找到以下Graph实现:
class Vertex:
def __init__(self,key):
self.id = key
self.connectedTo = {}
def addNeighbor(self,nbr,weight=0):
self.connectedTo[nbr] = weight
def getConnections(self):
return self.connectedTo.keys()
def getId(self):
return self.id
def getWeight(self,nbr):
return self.connectedTo[nbr]
class Graph:
def __init__(self):
self.vertList = {}
self.numVertices = 0
def addVertex(self,key):
self.numVertices = self.numVertices + 1
newVertex = Vertex(key)
self.vertList[key] = newVertex
return newVertex
def getVertex(self,n):
if n in self.vertList:
return self.vertList[n]
else:
return None
def addEdge(self,f,t,cost=0):
if f not in self.vertList:
nv=self.addVertex(f)
if t not in self.vertList:
nv=self.addVertex(t)
self.vertList[f].addNeighbor(self.vertList[t], cost)
def getVertices(self):
return self.vertList.keys()
def __iter__(self):
return iter(self.vertList.values())
def main():
g=Graph()
for i in range(6):
g.addVertex(i)
g.addEdge(0,1,5)
g.addEdge(1,5,4)
g.addEdge(5,3,6)
g.addEdge(3,4,5)
for v in g:
for w in v.getConnections():
print v.getId(),",",w.getId(),",",v.getWeight(w)
if __name__=="__main__":
main()
The program executes fine, but I was wondering if the author put some redundant parts, like in the functions addEdge()
and addVertex()
. 该程序执行良好,但我想知道作者是否放置了一些多余的部分,例如在函数addEdge()
和addVertex()
。
For what I see addEdge has an assignment that it never uses: 对于我所看到的,addEdge具有从未使用的分配:
nv=self.addVertex(t)
also the part that says: 还有说的部分:
if t not in self.vertList:
nv=self.addVertex(t)
in the same method does not do anything, and the variable nv is not used at all. 在相同的方法中什么也没做,并且变量nv根本不使用。 For what I see this is the implementation of a directed graph so if I want to program a non-directed graph it will suffice to put: 对于我所看到的,这是有向图的实现,因此,如果我要编写无向图,则只需放置以下内容即可:
self.vertList[t].addNeighbor(self.vertList[f], cost)
So I can also get rid of the return newVertex in the addVertex function. 因此,我也可以摆脱addVertex函数中的返回newVertex。 I have done those modifications and the program works still fine. 我已经做了这些修改,程序仍然可以正常工作。 Would those modifications be good and not bring any strange behaviour when I reuse this class? 当我重用该类时,这些修改会很好并且不会带来任何奇怪的行为吗?
And one last question, in the part that says: 最后一个问题,说的是:
for v in g:
for w in v.getConnections():
print v.getId(),",",w.getId(),",",v.getWeight(w)
it seems it only iterates over those values in the dictionary of G that has values and not with the empty ones (I mean those that have only a key), is it like that? 似乎只迭代G字典中具有值的值,而不是空值(我的意思是仅具有键的值),是这样吗?
Yes, I think nv=
is redundant but self.addVertex(f)
is necessary cause you need to add vertex. 是的,我认为nv=
是多余的,但是self.addVertex(f)
是必需的,因为您需要添加顶点。
Adding self.vertList[t].addNeighbor(self.vertList[f], cost)
will make a non-directed graph, true. 添加self.vertList[t].addNeighbor(self.vertList[f], cost)
将使一个无向图为true。
it seems it only iterates over those values in the dictionary of G that has values and not with the empty ones (I mean those that have only a key), is it like that? 似乎只迭代G字典中具有值的值,而不是空值(我的意思是仅具有键的值),是这样吗?
No, it will iterate all vertexes but only those with connections(edge) will generate output. 不,它将迭代所有顶点,但是只有那些具有连接(边)的顶点才会生成输出。
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