How can I use a list comprehension to extend a list in python? [duplicate]

Question

I'm not experienced in Python, and I often write code that (simplified) looks like this:

accumulationList = []
for x in originalList:
    y = doSomething(x)
    accumulationList.append(y)
return accumulationList

Then after my test passes, I refactor to

return [doSomething(x) for x in originalList]

But suppose it turns out a little different, and my loop looks like this:

accumulationList = []
for x in originalList:
    y = doSomething(x)
    accumulationList.extend(y)
return accumulationList

where the doSomething list returns a list. What is the most Pythonic way to accomplish this? Obviously, the previous list comprehension would give a list of lists.

Answer 1

Much simpler and cleaner with list comprehension:

[y for x in originalList for y in doSomething(x)]