Question

Say I have a Graph class and a Vertex class, defined as below

Graph.py

class Graph:

def __init__(self):
    self.adjacencyList = {}

def __str__(self):
    return str(self.adjacencyList)

def addVetex(self,key,value):
    if Vertex(key,value) not in self.adjacencyList:
        self.adjacencyList[Vertex(key,value)] = []

Vertex.py

class Vertex:
def __init__(self,key,value):
    self.key = key
    self.value = value

def __str__(self):
    return "Key: ",str(self.key)," Value: ",str(self,value)

def __hash__(self):
    return self.key

if I do this:

G = Graph()
G.addVetex(1,None)
G.addVetex(2,None)
G.addVetex(1,3)
print G

It print out {<Vertex.Vertex instance at 0x110295b90>: [], <Vertex.Vertex instance at 0x110295bd8>: []} But I am expecting something like {"Key:1 Value:None":[]...}

My question is what I am doing wrong? When a diction got print out, why it does not try to call the str function of its keys/values?

Thanks.

Answer 1

I believe the method you want to implement to get the string you want with your current code is Vertex.__repr__, which is what the python dictionary uses to get string representations of keys.

Here’s a related stackoverflow answer that sheds some light on the difference between __repr__ and __str__