Understanding the word destroys the list of keys

Question

I am trying to implement a ranked voting system in Python. I have this code:

import numpy as np
import itertools

candidates = ['Bob', 'Alice', 'Jim', 'Sarah', 'Paul', 'Jordan']

votes = np.matrix(
    '1 2 5 3 4 6;' \
    '1 2 3 4 5 6;' \
    '5 1 2 4 3 6;' \
    '6 2 1 3 4 5;' \
    '4 3 2 1 5 7'
    )

pairs = itertools.combinations(candidates, 2)  # All pairs of candidates

d = dict.fromkeys(pairs, 0)

for pair in pairs:
    print(pair)

Dictionary:

d
=> {('Paul', 'Jordan'): 0, ('Alice', 'Sarah'): 0, ('Alice', 'Jim'): 0, ('Alice', 'Paul'): 0, ('Jim', 'Sarah'): 0, ('Sarah', 'Paul'): 0, ('Bob', 'Alice'): 0, ('Bob', 'Jordan'): 0, ('Jim', 'Jordan'): 0, ('Jim', 'Paul'): 0, ('Sarah', 'Jordan'): 0, ('Bob', 'Paul'): 0, ('Bob', 'Sarah'): 0, ('Bob', 'Jim'): 0, ('Alice', 'Jordan'): 0}

This is what I want. But it seems that it destroys a list of tuples pairs.

If I select a dictionary line, the output of the code is:

('Bob', 'Alice')
('Bob', 'Jim')
('Bob', 'Sarah')
('Bob', 'Paul')
('Bob', 'Jordan')
('Alice', 'Jim')
('Alice', 'Sarah')
('Alice', 'Paul')
('Alice', 'Jordan')
('Jim', 'Sarah')
('Jim', 'Paul')
('Jim', 'Jordan')
('Sarah', 'Paul')
('Sarah', 'Jordan')
('Paul', 'Jordan')

Nothing is printed on the dictionary string.

I also tried to understand the dictionary

d = {pair: 0 for pair in pairs}

And the same thing happened. Why is the list destroyed pairs?

Answer 1

, , . dict.fromkeys , , StopIteration,

, :

pairs = list(itertools.combinations(candidates, 2))

Answer 2

pairs , . , fromkeys , pairs . , ( @chepner) , , ; .

pairs , itertools.tee:

pairs1, pairs2 = itertools.tee(itertools.combinations(...))

, - .

pairs , .