recursion problem with nested lists in python

问题

I have the following code:

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

When I call flat_list([1, [2, 2, 2], 4]), I expect it to return unpacked list ([1, 2, 2, 2, 4]). Instead it returns ([1, 4]). Although, if I try (print i) instead of (d.append(i)), it returns unpacked i.

I read an article about recursion, it says return needs to be after base condition.

How do I use kindda (return d.append(i))?

回答1:

you call your function, but don't do anything with its return value when calling it recursively

    else:
        d.extend(flat_list(i))

extend will take all the items from the list that flat_list returns, and adds them to your list you are creating within the function

Example

来源：https://stackoverflow.com/questions/58606878/recursion-problem-with-nested-lists-in-python