'str' object has no attribute / error calling a dictionary

Question

I have a class with a function that adds an edge to the graph, according to the input given. For example: if the input is add James Larry 1, an edge will be added between James and Larry with the weight (intimacy level) 1. The graph is a dictionary of sets, so, the keys are the node and the values (sets) are the edges.

So, this function has as parameters: the source, the destination and the weight. The class is represented below:

class DiGraph(object):

     # Create an empty graph.
    def __init__(self):
        ## A dictionary that stores an entry of a node, as the key, and a set of outgoing edges 
        # (destination node, weight) from the node, as its value.
        self.graph = {}

        ## Total number of edges in the graph.
        self.__numEdges = 0

        ## The largest edge distance.
        # self.__infinity = sys.maxint
        self.__infinity = sys.maxsize

        ## Holds the path from a source node to a given node.
        self.__pathToNode = None

        ## Accumulated distance from source to a node.
        self.__dist = None

### (...)

   def addEdge(self, src, dst, c=1):
        if ( src == None or dst == None or c <= 0 or src == dst ):
            return False

       # the edge set of src
        eSet = self.graph.get(src)
        e = Edge(dst,c) # new edge
        if eSet == None: 
            # no edge starting at src, so create a new edge set
            eSet = set()
            self.__numEdges += 1
        else:
            ed = self.getEdge(src,dst)
            if ( ed != None ):
                ed.setCost(c)
                return True
            else:
                self.__numEdges += 1

        eSet.add(e) # a set does not have duplicates

        self.graph[src] = eSet
        if not self.hasVertex(dst):
            self.addVertex(dst)

        return True

I am trying to implement this code:

import DiGraph

#Create an empty graph
def main():
    aGraph = {}

    f = open("infile.txt")
    contents = f.read()
    lines = contents.splitlines()

    word = []

    for line in lines:
        word.append(line.split())

    for i in range(len(word)):
        if word[i][0] == 'add':
            aGraph = DiGraph.DiGraph.addEdge(word[i][1], word[i][2], int(word[i][3]))

    return aGraph

grafo = main()

And the first line of the file is: add James Larry 1

This error is being showed to me when I try to run this code:

Traceback (most recent call last):

File "C:/.../SocialGraph.py", line 24, in

grafo = main()

File "C:/.../SocialGraph.py", line 20, in main

aGraph = DiGraph.DiGraph.addEdge(word[i][1], word[i][2], int(word[i][3]))

File "C:...\DiGraph.py", line 156, in addEdge

eSet = self.graph.get(src)

AttributeError: 'str' object has no attribute 'graph'

What can I do to correct this?

Answer 1

You implement addEdge as an instance method so that you have to create an instance to use it. Like so:

# create DiGraph instance
diGraph = DiGraph.DiGraph()

for i in range(len(word)):
        if word[i][0] == 'add':
            aGraph = diGraph.addEdge(word[i][1], word[i][2], int(word[i][3]))

Answer 2

DiGraph.DiGraph.addEdge(word[i][1],

You call this as a static method. 'word[i][1]' becomes 'self'.