Simplified python list comprehension using for

Question

i have following python list comprehension and it's hard for me to understand it

set([device for room, devices in home.items() for device in devices['devices'] + device_synonyms])

I need to simplified it using for operator

home = {'Гостиная': {'devices': ['Мак', 'Основной', 'Ночник']}, 'Коридор': {'devices': ['Роутер', 'Вход', 'Шкаф', 'Вешалка']}, 'Спальня': {'devices': ['Ночник']}}

The expected result should be

{'Вход', 'Ночник', 'Шкаф', 'Вешалка', 'Основной', 'Роутер', 'Мак'}

Does this answer your question? [Understanding nested list comprehension](https://stackoverflow.com/questions/8049798/understanding-nested-list-comprehension) — rchome, Dec 10 '21 at 06:53
Note: there is no need for this to be a list comprehension. You can feed a generator expression to `set`. — Chris, Dec 10 '21 at 06:56
@Chris you mean something like set((device for room, devices in home.items() for device in devices['devices'] + device_synonyms)) — Alex Nikitin, Dec 10 '21 at 06:57
Almost. You can elide a set of parentheses. `set(device for room, devices in home.items() for device in devices['devices'] + device_synonyms)` — Chris, Dec 10 '21 at 06:59

Jonathan Weine · Answer 1 · 2021-12-14T07:56:26.107

2

The exact translation of the listr comprehension to a for loop is given by:

l = []
for room, devices in home.items():
   for device in devices["devices"] + device_synonyms:
       l.append(device)
s = set(l)
print(s)

As pointed out by chris, there is no need to use the intermediate list:

s = set()
for room, devices in home.items():
   for device in devices["devices"] + device_synonyms:
       s.add(device)
print(s)

edited Dec 14 '21 at 07:56

answered Dec 10 '21 at 06:54

Jonathan Weine

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3
11

1

There's no need for the intermediate `l` list. You can create `s`, then add to it in the loop with `s.add(device)`. – Chris Dec 10 '21 at 06:59
That's true chris, thanks for the addition. I wanted to exactly replicate the comprehension line for demonstration purpose. – Jonathan Weine Dec 10 '21 at 07:03

score 0 · Answer 2 · answered Dec 10 '21 at 07:06

You don't use room and you don't have to append device_synonyms multiple times as duplicates will be removed by set() anyway. So the code can be simplified and rewritten as:

result = set(device_synonyms)
for devices in home.values():
    result |= set(devices['devices'])

Simplified python list comprehension using for

2 Answers2