Python在多维字典中添加数据

Question

while (E > 0):
    line = raw_input("enter edges : ")
    data = line.split()
    mygraph[data[0]] = {data[1] : data[2]} //this line 
    print mygraph
    E-=1

Desired data structure:

mygraph = { 
        'B': {'A': 5, 'D': 1, 'G': 2}
        'A': {'B': 5, 'D': 3, 'E': 12, 'F' :5}}

i want to add multiple entries for same key like but mycode is taking only one value for one node and then replacing the entries.How to do that?

Answer 1

You need to first add an empty dictionary for the key data[0] if it doesn't already exist, then add the values to it. Otherwise you just wipe out it out every time you loop.

The two usual ways are either to use setdefault on a normal dictionary:

mygraph.setdefault(data[0], {})[data[1]] = data[2]

or use collections.defaultdict where the default is an empty dictionary:

>>> from collections import defaultdict

>>> mygraph = defaultdict(dict)

>>> edges = [[1, 2, 3], [1, 3, 6]]
>>> for edge in edges:
...     mygraph[edge[1]][edge[2]] = edge[3]

>>> mygraph
{1: {2: 3,
     3: 6}}

Answer 2

Replace this line:

mygraph[data[0]] = {data[1] : data[2]}

with these:

if not data[0] in mygraph:
    mygraph[data[0]] = {}
mygraph[data[0]][data[1]] = data[2]