Element wise, variable combination of lists in python

Question

I want to write to code to have the following behavior:

[ 1, 1, ["Alpha"]]
+
[ 2, 2, ["Beta"] ]
||       ||     ||
\/       \/     \/
[3, 3, ["Alpha", "Beta"]]

in python. Is this possible without very messy comprehensions and mapping?

Voting to close as duplicate since the answers given (and the pythonic answers) are duplicates of the linked question. The short answer is `yes`, you can avoid maps/comprehension using loops. — Snakes and Coffee, Jul 24 '17 at 21:13
I will also add, since no one has added this answer, that you can use reduce and a custom lambda for aggregating any number of weird data types. — Erich, Sep 12 '19 at 19:25

score 7 · Answer 1 · answered Jul 24 '17 at 21:12

7

[a + b for a, b in zip(l1, l2)]

answered Jul 24 '17 at 21:12

Luckk

Indeed. I'd be interested to know if the OP thinks it's a "messy comprehension". – Eric Duminil Jul 24 '17 at 21:17
I believe in an older version of python that this did not work for custom defined classes, or that it at least didn't work for my use case because I tried this and it failed. I forget that use case now unfortunately, but this does now work, at least for my machine. – Erich Sep 12 '19 at 19:23

cs95 · Accepted Answer · 2019-04-29T10:23:10.407

3

Yes, it is possible, though I'd think twice before calling list comprehensions messy. Pass operator.__add__ to map along with the two lists:

import operator
list(map(operator.__add__, l1, l2))
# [3, 3, ['Alpha', 'Beta']]

edited Apr 29 '19 at 10:23

answered Jul 24 '17 at 21:10

cs95

1

You can just use `operator.add` – juanpa.arrivillaga Jul 24 '17 at 21:24
1

@juanpa.arrivillaga I was trying to be a special snowflake. – cs95 Jul 24 '17 at 21:26
operator.__add__ answers my question better. I've accepted this question because of this. – Erich Jul 24 '17 at 22:39
@Erich I believe add and __ add __ do the same thing :) – cs95 Jul 24 '17 at 22:41
For this purpose yes. But if you define `__add__` in a class then the behavior will not be the same as add. Which is more of what I was asking but it's a bit after the fact. – Erich Jul 24 '17 at 22:54
@Erich Fair enough. Will rollback my answer. – cs95 Jul 25 '17 at 05:00

score 2 · Answer 3 · answered Jul 24 '17 at 21:11

2

This solution uses list comprehensions, although they are, imo, far from messy. Also, it is pretty readable and doesn't require a library

a = [1, 1, ["ALPHA"]]
b = [2, 2, ["BETA"]]
c = [a[i]+b[i] for i in range(len(a))]
print(c)

answered Jul 24 '17 at 21:11

Sam Craig

3 Answers3