How does the list comprehension to flatten a python list work?

Question

I recently looked for a way to flatten a nested python list, like this: [[1,2,3],[4,5,6]], into this: [1,2,3,4,5,6].

Stackoverflow was helpful as ever and I found a

Answer 1

For the lazy dev that wants a quick answer:

>>> a = [[1,2], [3,4]]
>>> [i for g in a for i in g]
[1, 2, 3, 4]