How can I add key values into a dictionary from reading in each line of a .txt file and update values?

Question

I'm kind of new to python so I'm trying pick it up. If I had a .txt file like this:

A B
A C
A E
B D
C D
C F
D G
F C
G H

And I read in the .txt file line by line with:

with open(txtFile) as file:
                for line in file:

I want it so that if the letter doesnt exist, then create it but if it does, itll add the letter it connects to, onto that existing letter. How would I be able to create a dictionary that maps everything so it ends up looking like this:

graph = {
        'A': ['B', 'C', 'E'],
        'B': ['D'],
        'C': ['D', 'F'],
        'D': ['G'],
        'F': ['C'],
        'G': ['H']
        }

This is basically all I have right now:

graph = {}

        with open(txtFile) as file:
                for line in file:
                        line.split()

        graph.append

I dont know how to actually add keys into the dictionary. But I guess once the keys are in I can just use something like:

graph['A'].append(line[1])

right? Also, would I have to use a snippet of code that traverses all the keys in the dictionary in order to see if that key already exists? Or will duplicates just not work?

Answer 1

Try this (not tested code):

from collections import defaultdict

graph = defaultdict(list)

with open(txtFile) as file:
    for line in file:
        s_line = line.split()
        graph[s_line[0]].append(s_line[1])