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Please look at the following Pyton code:
vec = [ [1, 2, 3], [4, 5, 6], [7, 8, 9] ]
flat1 = [ num for elem in vec for num in elem]
flat2 = [ num for num in elem for elem in vec]
flat1 = [ 1, 2, 3, 4, 5, 6, 7, 8, 9]
Fair enough!
But
flat2 = [ 7, 7, 7, 8, 8, 8, 9, 9, 9]
Why is it like that? ...