如何在python中一次将两个值附加到字典？

Question

I don't think the title really explains it, but here's the problem.

My code is this (Python 2.7):

    Dict = {}
    for i in range(0, 6):
        for j in range(0, 7):
            Dict[i][j] = 0;
    return Dict;

But I always get KeyError: 0.

Answer 1

Here, set one at a time:

mydict = {}
for i in range(0, 6):
    mydict[i] = {}

    for j in range(0, 7):
        mydict[i][j] = 0

return mydict

That is, if you want something like this:

{
    0:{
        0: 0,
        // ...
    },
    // ...
}

The problem you were running into is that you were trying to set an item of an item, before defining what the i-th item was.

Answer 2

Use a defaultdict:

from collections import defaultdict

a = defaultdict(dict)

for i in range(0, 6):
    for j in range(0, 7):
        a[i][j] = 0

Answer 3

In python you have to explicitly define each index in a dictionary. You can have them auto created for you like this

import collections
auto_dict = lambda: collections.defaultdict(auto_dict)

my_dict = auto_dict()
my_dict['lvl1']['lvl2'] = 1
print my_dict['lvl1']['lvl2']
# 1