Python - 从文本文件到字典的邻接列表

Question

With networkx i am able to generate a text file which represents an adjacency list of a graph. I need to convert the text file into a dictionary. So the key is the left most number on each line, and it is a list of values for the rest of the numbers to the right on the line. The value list can sometimes be empty. We can call the input file test.txt. Thanks!

For example, this is what im looking for: {1: [], 2: [3,7], 3: [4,7,9], 4: [7,9], 9: []}

This is the text file generated to be converted:

#adjlist.py
# GMT Tue May 26 14:48:55 2020
# 
1
2 3 7
3 4 7 9
4 7 9
7 9
9

Answer 1

Reading a text file is trivial with the open() function. I suggest using the .read() method rather than iterating over the open file to read lines as reading the file in bulk into memory is much faster than iterating over the lines from the file on disk. That is of course if the file is smaller than your RAM. .strip() returns a copy of the string with leading and trailing characters remove. .split() splits with the delimiter given, here we use \n to split the file to lines.

Finally, we iterate over each line and call .split() on the line, this time splitting by space. This returns a list of items, where the [0] indexed item will be your key and the rest ( [1:] ) will be your values.

You can use a defaultdict from the collections built-in library to achieve multiple items to a single dictionary key.

from collections import defaultdict

with open("test.txt") as f:
    lines = f.read().strip().split("\n")

d = defaultdict(list)

for line in lines:
    ls = line.split(" ")
    d[ls[0]] = ls[1:]