将变量指定为列表而不在函数中覆盖它 [英] Designate a variable as a list without overwriting it in a function

问题描述

我创建了一个函数，可以将嵌套列表展平为普通列表.

I created a function that will flatten a nested list into an ordinary list.

outputarray = []

def flattenarray(x):
    for elmt in x:
        if isinstance(elmt, float) or isinstance(elmt, int):
            outputarray.append(elmt)
        elif isinstance(elmt, list):
            flattenarray(elmt)
    return outputarray

上面的方法很完美，但是我试图在函数中包含"outputarray"变量，但是当我这样做时，递归步骤将把outputarray列表改写为空列表.

The above works perfectly, but I am trying to have the "outputarray" variable inside the function, but when I do, the recursion step will overwrite the outputarray list back into an empty list.

我该如何在函数内部指定一个列表，同时又能在不递归的情况下将其追加到列表中?

How can I make this work to designate a list inside the function and at the same time be able to append to it without overwriting it during recursion?

推荐答案

您将要在函数中创建输出数组.一种进行方式是在递归步骤中传递输出容器:

You will want to create the output array from within the function. One way to proceed is to pass the output container along in the recursive step:

def flattenarray(x, outputarray=None):
    if outputarray is None:
        outputarray = []
    for elmt in x:
        if isinstance(elmt, float) or isinstance(elmt, int):
            outputarray.append(elmt)
        elif isinstance(elmt, list):
            flattenarray(elmt, outputarray=outputarray)
    return outputarray

更Python化的方法是使拼合器逐个生成项目.请注意，isinstance可以接受类型的元组，因此您只需调用一次即可.

A more Pythonic approach is for the flattener to yield the items one-by-one. Note that isinstance can accept a tuple of types, so you only need to call it once.

def flatten(x):
    for elmt in x:
        if isinstance(elmt, (int, float, str, bytes)):
            yield elmt
        else:
            yield from flatten(elmt)

更正确的鸭式实现:

def flatten(x):
    try:
        it = iter(x)
    except TypeError:
        yield x
        return
    if isinstance(x, (str, bytes)):
        yield x
        return
    for elem in it:
        yield from flatten(elem)

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