在python 3中创建嵌套的dicts

Question

I'm trying to create the following nested dict structure, {0: {0: 1}, 1: {0: 1, 1: 1}} with the following code:

feats = {}
for i in range(2):
    feat = feats.get(i, {})
    for j in range(i+1):
        feat[j] = 1

but all I'm getting feats = {} . Why is that? Thanks.

Answer 1

The problem here is, you are not storing feat value in feats , so it is lost after every iteration. At the end of the iterations, feats is empty.

You can fix your code like below:

feats = {}
for i in range(2):
    feat = feats.get(i, {})
    for j in range(i+1):
        feat[j] = 1
    feats[i] = feat

print(feats)

output:

{0: {0: 1}, 1: {0: 1, 1: 1}}

Answer 2

First of all I ran your program and I printed feats, it printed{0: 1, 1: 1} and not {}

Second thing, what I can understand from your requirement is that, in a generic way, while looping through a range of numbers, you want to have that number as key and value as dictionary containing key value pairs, where number of keys are from 0 to that number and value as 1. Correct me if I am wrong.

So the correct program for this would be:

feats = {} 
for i in range(2): 
   feats[i] = feats.get(i, {}) 
   for j in range(0,i+1): 
      feats[i][j] = 1
print feats 

You can replace 2 with any number in range and get your answer accordingly.