synthax question

[aka]

Hi,

I have a long experience in computing but not in python. I need to understand this :

combinableLayers=[l for l in combinableLayers if len(l)>1 ]

I have of course found what is a list, what is a for loop but impossible to understand this line, especially " l for l .."

Can someone please help me ?

Thanks && regards

aka

[DPaul]

Take a look at what those pythonistas call "list comprehension" :-)

Paul

[snippsat]

Written as normal for loop.

combinableLayers = ([0, 1, 2], [9], [7, 8])
new_lst = []
for l in combinableLayers:
    if len(l) > 1:
        new_lst.append(l)

print(new_lst)

Output:
[[0, 1, 2], [7, 8]]

In Python list comprehension is a common and alternative syntax to make it in one expression.

combinableLayers = ([0, 1, 2], [9], [7, 8])
combinableLayers = [l for l in combinableLayers if len(l) > 1]
print(combinableLayers)

Output:
[[0, 1, 2], [7, 8]]

[aka]

Thanks, I reached the first step. For the second one, take please a look :

combinableLayers=[[l for l in g.layers if l.visible] for g in image.layers if g.visible and isinstance(g,gimp.GroupLayer)]

I found some help searching "nested list comprehension" but it is here not enought, I see 'g' in the inner and the outer list.

Is it the same 'g', is it a "correled nested list comprehension" ? How does that work ? I please need to be sure. :)

I attached the whole script (see too https://www.gimp-forum.net/Thread-ofn-ex...mbinations).

[snippsat]

combinableLayers=[[l for l in g.layers if l.visible] for g in image.layers if g.visible and isinstance(g,gimp.GroupLayer)]

I see 'g' in the inner and the outer list.
Is it the same 'g', is it a "correled nested list comprehension" ? How does that work ?

The g is local to list comprehension,what's take in for outside is image.layers then both do a test against this image.layers.
The code in ofn-export-layers-combinations.py is written in Python 2 in 2021,which is outdated as support for Python 2 officially stopped January 1 2020.