recursion problem with nested lists using yield in python [duplicate]

Question

I have a code as below and I need it to unpack lists using yield:

def flat_list(array):
    d=[]
    for i in array:
        if not isinstance(i, list):
            yield i
        else:
            flat_list(i)

For example, flat_list([1, [2, 2, 2], 4]) should return [1, 2, 2, 2, 4]. My code returns [1, 4].

I understand from previous question that I need not only recursively call a function, but to specify what it should do.

But how do you add flat_list(i) items to yield items? Something like flat_list(i).extend(yield i).

d is unused. You don't need to fill a list in your function when you yield — Mad Physicist
– Mad Physicist, Commented Oct 29, 2019 at 13:27

Kevin · Accepted Answer · 2019-10-29 13:34:03Z

5

You should yield all of the items generated by the flat_list(i) call. You can do this with yield from.

def flat_list(array):
    for i in array:
        if not isinstance(i, list):
            yield i
        else:
            yield from flat_list(i)

for x in flat_list([1, [2, 2, 2], 4]):
    print(x)

Result:

edited Oct 29, 2019 at 13:34

answered Oct 29, 2019 at 13:26

Kevin

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2 Comments

Dan Over a year ago

What's d=[] for?

Kamal Valikhanov Over a year ago

mistake, from old draft code

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