Idiom for flattening a shallow nested list: how does it work?

Question

I found this bit of code in a module I am working on:

l = opaque_function()
thingys = [x for y in l for x in y]

I can\'t read this. By expe

Answer 1

lis=[x for y in l for x in y] is Equivalent to:


lis=[]
for y in l:
   for x in y:
      lis.append(x)