Python: Append same element to multiple lists

Question

I have a snippet of code that repeats itself and is annoying/looks ugly. I have 4 lists and I need to add "nan" to all multiple times at different points of code. It looks like this:

a, b, c, d = []

...

a.append(np.nan)
b.append(np.nan)
c.append(np.nan)
d.append(np.nan)

...

I would like a more elegant solution (single-line) to append nan to all those lists.

Any ideas?

Finn · Accepted Answer · 2022-01-21 13:37:53Z

3

In could be written in one line, but it looks terrible.

[cur_list.append(np.nan) for cur_list in [a,b,c,d]]

I would recommend at least 2 lines, to have some readability.

for cur_list in [a,b,c,d]:
    cur_list.append(np.nan)

answered Jan 21, 2022 at 13:37

Finn

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2 Comments

rpin Over a year ago

Wow that was fast, thx! Readability is precisely what I am going for, so using solution #2 above. Got stuck because of ugly code, now trying to untangle to understand a bug in the logic. I haven´t been able to run it but sure this does the trick... I will a comment later in case I run into trouble, thanks!

pabouk - Ukraine stay strong Over a year ago

Please do not use the first code. It is a misuse of a list comprehension for side-effects. I do not understand the urge to squeeze some code to a single line :( If you really want to have the code on a single line, use the for loop (single-command body can be on the same line) ----------------------------------------------------- for cur_list in [a, b, c, d]: cur_list.append(np.nan)

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