Python 嵌套字典更新循环

Question

The following code would generate a nested dictionary. But

   l = [1,2,3,4]
   n_dict = current = {}
   for n in l:
      current[n] = {}       # would n_dict get update?
      # print(current)      # just to check
      # print(n_dict)       # just to check
      current = current[n]  # would n_dict get update?
      # print(current)      # just to check
      # print(n_dict)       # just to check
   print(n_dict)

n_dict has become a nested dictionary while current is not. So what's the rule that n_dict will or will not get update inside the foo-loop (see the two question lines)?

Thanks

Answer 1

Let me tell you how the above code is working -

n_dict = current = {}

When you do this both n_dict and current will point to the same empty dictionary.

Now, in for loop, see this line -

current = current[n]

Here, you're changing the current variable it now points to an empty dict. You're using the current variable to modify the original dict and that original dict can be access by n_dict pointer.