在 for 循环中将动态字典附加到 Python 中的列表

Question

This is initial program for implementing Prefix Tree for a Question. Later i used the dict.copy() function to deal with dynamic behavior of dictionary, but couldn't get the desired output .

end='end'
def make_trie(word,root):
    current_dict=root
    for letter in word:
        current_dict=current_dict.setdefault(letter,{})
    current_dict[end]=end
    return root

s=[]
n=int(input())
t=[]
for _ in range(n):
    s.append(input())

    if  _==0:
        d=make_trie(s[-1],{})

    else:
        d=make_trie(s[-1],d)
    t.append(d.copy())
print(t)

List i am getting for input : 4 abcd abce abcdex abcde
is :
[{'a': {'b': {'c': {'d': {'end': 'end', 'e': {'x': {'end': 'end'}, 'end': 'end'}}, 'e': {'end': 'end'}}}}}, {'a': {'b': {'c': {'d': {'end': 'end', 'e': {'x': {'end': 'end'}, 'end': 'end'}}, 'e': {'end': 'end'}}}}}, {'a': {'b': {'c': {'d': {'end': 'end', 'e': {'x': {'end': 'end'}, 'end': 'end'}}, 'e': {'end': 'end'}}}}}, {'a': {'b': {'c': {'d': {'end': 'end', 'e': {'x': {'end': 'end'}, 'end': 'end'}}, 'e': {'end': 'end'}}}}}]
Which is 4 times the final Dictionary.
Please suggest some way to deal with this issue.

Answer 1

Since the trie is a dictionary of dictionaries, you need to deep copy instead of shallow. Try this:

from copy import deepcopy  

end='end'
def make_trie(word,root):
    current_dict=root
    for letter in word:
        current_dict=current_dict.setdefault(letter,{})
    current_dict[end]=end
    return root

s=[]
n=int(input())
t=[]
for _ in range(n):
    s.append(input())

    if  _==0:
        d=make_trie(s[-1],{})

    else:
        d=make_trie(s[-1],d)
    t.append(deepcopy(d))
print(t)  

When you shallow copy, you just copy the outermost dictionary, so the inner dictionaries are still shared between copied dictionaries.

Answer 2

Another option would be to cast the dictionary object to a string and back, using the Python 3's eval function or the inbuilt ast library's function literal_eval, if your dictionary is not too big. You can try the following:

end='end'
def make_trie(word,root):
    current_dict=root
    for letter in word:
        current_dict=current_dict.setdefault(letter,{})
    current_dict[end]=end
    return root

s=[]
n=int(input())
t=[]
for _ in range(n):
    s.append(input())

    if  _==0:
        d=make_trie(s[-1],{})

    else:
        d=make_trie(s[-1],d)

    d_str = str(d)   
    t.append(eval(d_str))
print(t)