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pythonpython-2.7python-itertoolsfunction-composition
JohnJ
JohnJ

Reputation: 7056

python "multiple" combine/chain list comprehension

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!

Upvotes: 1

Views: 3674

Answers (3)

gariel
gariel

Reputation: 687

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

Upvotes: 1

John La Rooy
John La Rooy

Reputation: 304365

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]

Upvotes: 6

Thomas Fenzl
Thomas Fenzl

Reputation: 4392

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.

Upvotes: 6

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