(Write a Python program) Write a recursive function flatten. The function accept

Question

(Write a Python program)

Write a recursive function

flatten. The function accepts a deeply nested list xs and transforms it

into a single-level list. You do not know how deeply the list is nested.

Here are sample calls:

print(flatten([[10, 200], 300, 40]))

print(flatten([-5, [30, [10, 50]], -50]))

print(flatten([4, [10, 20], [180, 30], 40]))

print(flatten([10, [10, [300, 400]], [20, 30]]))

Here are the resutls:

[10, 200, 300, 40]

[-5, 30, 10, 50, -50]

[4, 10, 20, 180, 30, 40]

[10, 10, 300, 400, 20, 20]

You can use the built-in function type() to determine if an item is a list. For example, if x is [10, 20], then the expression type(x) == list evaluates to True. On the other hand, if x is 10, then

type(x) == list evaluates to False.

Explanation / Answer

>>>def flatten(lst):
return sum( ([x] if not isinstance(x, list) else flatten(x) // checks whether x is an instance in the for x in lst), [] ) list

>>>flatten([[10, 200], 300, 40])

>>>[10, 200, 300, 40]

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