List comprehension: Returning two (or more) items for each item [duplicate]

Double list comprehension:

[f(x) for x in range(5) for f in (f1,f2)]

Demo:

>>> f1 = lambda x: x
>>> f2 = lambda x: 10*x

>>> [f(x) for x in range(5) for f in (f1,f2)]
[0, 0, 1, 10, 2, 20, 3, 30, 4, 40]

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