python "multiple" combine/chain list comprehension

Question

I am quite new to python and I have been learning list comprehension alongside python lists and dictionaries.

So, I would like to do something like:

[my_functiona(x) for x in a]

..which works completely fine.

However, now I’d want to do the following:

[my_functiona(x) for x in a] && [my_functionb(x) for x in a]

..is there a way to combine or chain such list comprehension? – where the second function uses the result of the first list. SHortly speaking, I would like to apply my_functiona and my_functionb sequentuially to list a

I did try googling this – but could not find anything satisfactory.
Sorry if this is a stupid 101 question!

Asked By: JohnJ

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Source

Answer 1

You just iterate over the result of the first comprehension:

def double(x):
    return x*2
def inc(x):
    return x+1

[double(x) for x in (inc(y) for y in range(10))]

I made the inner comprehension a generator expression as you don’t need to get the full list.

Answered By: Thomas Fenzl

Answer 2

You can compose the functions like this

[my_functionb(my_functiona(x)) for x in a]

The form in Thomas’ answer is useful if you need to apply a condition

[my_functionb(y) for y in (my_functiona(x) for x in a) if y<10]

Answered By: John La Rooy

Answer 3

[my_functiona(my_functionb(x)) for x in a]

Answered By: gariel

python "multiple" combine/chain list comprehension

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