你如何从for循环中提取元组的所有元素？

Question

I am trying to solve combinations(nCr) problem. I have the following numbers [1,2,3,4] . The code needs to produce all the possible combinations(4C2): (1,2), (1,3), (1,4), (2,3), (2,4), (3,4) . Here is the code:

import itertools
from math import factorial

def calc_combin(n, r):
    return factorial(n) // factorial(r) // factorial(n-r)

lines=calc_combin(4,2) #4C2

b_list = list(range(1,5))
combinations = itertools.combinations(b_list,2)

c_list=[]

for i_c in range(0,lines):
    c_list.append([])

for c in combinations:
    c                 #tuple that has all the combinations
    c_listi = list(c) #converting tuple "c" to list "c_listi"
    print(c_listi)

This is the output:

[1, 2]
[1, 3]
[1, 4]
[2, 3]
[2, 4]
[3, 4]

Now I want the output values to be stored outside the for loop. without overwriting the previous values.

Is there a way to extract all the tuple( c ) elements outside the for-loop? If not how do you extract it from list variable( c_listi ) outside the for-loop?

Answer 1

If you assign the contents of itertools.combinations to a variable as a list, you can reuse it as many times as you like:

cs = list(itertools.combinations(b_list,2))

If you need the contents to be lists, instead of tuples:

cs = [list(t) for t in itertools.combinations(b_list,2)]

After either, you can use and reuse cs as often as you like.