在Python3中解包可迭代对象? [英] Unpacking iterables in Python3?

问题描述

为什么返回in sort_tup_from_list for key, val in tup: ValueError: not enough values to unpack (expected 2, got 1)

# list with tuples
lst = [("1", "2"), ("3", "4")]

# sorting list by tuple val key
def sort_tup_from_list(input_list):
    tmp = []
    print(tup)
    for tup in input_list:
        for key, val in tup:
            tmp.append((val, key))
            tmp.sort(reverse=True)
    return tmp

print(sort_tup_from_list(lst))

当我注释掉第二个for循环时，它会打印出元组:

When I comment out second for loop, it prints tuple:

lst = [("1", "2"), ("3", "4")]
def sort_tup_from_list(input_list):
    tmp = []
    for tup in input_list:
        print(tup)
        # for key, val in tup:
        #     tmp.append((val, key))
        #     tmp.sort(reverse=True)
    return tmp

print(sort_tup_from_list(lst))

输出:

('1', '2')
('3', '4')
[]

因此，元组在那里.他们为什么不给自己拆包?

So, tuples are there. Why are they not unpacking themselfs?

推荐答案

您的第二个for循环正在遍历元组中的项目，但是您正在抓取其中的两个项目.我想这就是你想要的:

Your second for loop is looping through items in the tuple, but you're grabbing both of the items in it. I think this is what you want:

# list with tuples
lst = [("1", "2"), ("3", "4")]

# sorting list by tuple val key
def sort_tup_from_list(input_list):
    tmp = []
    print(tmp)
    for key,val in input_list:
        tmp.append((val, key))
        tmp.sort(reverse=True)
    return tmp

print(sort_tup_from_list(lst))

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