How to extend within list comprehensions

Question

Still trying to wrap my head around list comprehensions. Below, 'e' is a list. How would I write this as a list comprehension?

events = []
        for req in request:
            e = req[attr]
            events.extend(e)

I tried the following and it gave me a list of lists([[a,b],[c,d]] rather than a flat list [a, b, c, d]

events = [req[attr] for req in request]

```events = [val for req in request for val in req[attr]]```? — , Aug 06 '21 at 17:56
this is definitely a duplicate https://stackoverflow.com/a/3899658/14385360 — Einliterflasche, Aug 06 '21 at 17:58
Does this answer your question? [list.extend and list comprehension](https://stackoverflow.com/questions/3899645/list-extend-and-list-comprehension) — Einliterflasche, Aug 06 '21 at 18:00
You said you want a "flat list"; searching for `list comprehension flatten` [gives you multiple good answers right off the top, without even mentioning Python](https://duckduckgo.com/?q=list+comprehension+flat). — Karl Knechtel, Aug 06 '21 at 18:02
Please also specifcially see https://treyhunner.com/2015/12/python-list-comprehensions-now-in-color/ — Karl Knechtel, Aug 06 '21 at 18:03

score 1 · Accepted Answer · edited Aug 06 '21 at 17:57

1

You can use two generators in the list comprehension:

events = [val for req in request for val in req[attr]]

edited Aug 06 '21 at 17:57

chepner

answered Aug 06 '21 at 17:57

1

This works by breaking apart the list into elements and then place each element into the list? – nebula186 Aug 06 '21 at 17:58
Yes. It is a shorter form of nested loops and loops over every item of every sublist – Einliterflasche Aug 06 '21 at 17:59

1 Answers1