Question

假设我有一个变量结构如下：

results = [([123], 456),
 ([1, 2, 3], 456),
 ([2], 456)]

我希望使用字典理解将其放入字典中，我实现了这样做：

{item[1]:set(i for item in results for i in item[0]) for item in results}

{456: {1, 2, 3, 123}}

但现在假设变量results变为：

[([123], 456),
 ([1, 2, 3], 456),
 ([2], 456),
 ([789], 'fizz')]

我未能成功地改变理解以适应这种情况。如何通过使用字典理解来实现这一结果？我知道如何使用循环来完成它，但我希望通过理解来学习如何实现它。谢谢！

编辑：

输出如下：

{456: {1, 2, 3, 123}, 'fizz': {789}}

Answer 1

You can easily do this without a comprehension, but if you insist on a comprehension, here's a solution that uses itertools.groupby:

from itertools import groupby
import operator

f = operator.itemgetter(1)
r = {k: set(i for x in g for i in x[0]) for k, g in groupby(results, f)}
print(r)
# {456: set([3, 1, 2, 123]), 'fizz': set([789])}

Caveat: Note that no presorting is done, since the items are already arranged according to the group key.

The solution is more readable (say more Pythonic) with a simple for loop that uses defaultdict:

from collections import defaultdict

r = defaultdict(set)
for v, k in results:
   r[k].update(v)
print(r)
# defaultdict(<type 'set'>, {456: set([3, 1, 2, 123]), 'fizz': set([789])})

Answer 2

Here is a solution using only dictionary and set comprehension:

{b: {k for x, y in results for k in x if y == b} for a, b in results}

从列表中的字典理解，其中包含列表

2 个答案: