Question

在Python中，是否可以模仿JavaScript数组（即，在数组范围之外添加值时自动扩展的数组）？在JavaScript中，当在数组的索引之外分配值时，数组会自动扩展，但在Python中，它们不会：

theArray = [None] * 5
theArray[0] = 0
print(theArray)
theArray[6] = 0 '''This line is invalid. Python arrays don't expand automatically, unlike JavaScript arrays.'''

这在JavaScript中是有效的，我试图在Python中模仿它：

var theArray = new Array();
theArray[0] = 0;
console.log(theArray);
theArray[6] = 0; //the array expands automatically in JavaScript, but not in Python

Answer 1

如果你真的需要，你可以定义这样的结构：

class ExpandingList(list):
    def __setitem__(self, key, value):
        try:
            list.__setitem__(self, key, value)
        except IndexError:
            self.extend((key - len(self)) * [None] + [value])

>>> a = ExpandingList()
>>> a[1] = 4
>>> a
[None, 4]
>>> a[4] = 4
>>> a
[None, 4, None, None, 4]

将它与其他python功能集成可能很棘手（负索引，切片）。

Answer 2

zch has already given a great answer，但我会发布此信息，向您展示如何复制获取的行为

class MyList(list):
    @property
    def length(self): # for the example bracket notation
        return len(self)
    def __getitem__(self, key): # Fix GET
        try: # assume permission
            return list.__getitem__(self, key)
        except (IndexError, TypeError): # "ask forgiveness"
            pass # using pass to save indents as try was a return
        if key == 'length': # example bracket notation for length getter
            return self.length
        try: # JavaScript doesn't care about number type and accepts
            key = int(key) # strings, too, but Python req.s integers
            return list.__getitem__(self, int(key))
        except (IndexError, ValueError):
            pass
        return None
    def __setitem__(self, key, value): # Fix SET
        try:
            list.__setitem__(self, key, value)
            return value # copy return behaviour
        except (IndexError, TypeError):
            pass
        try:
            key = int(key) # force int
        except ValueError:
            return # fail quietly?
        if key < 0: # still throw for bad key
            raise IndexError()
        self.extend((key - len(self)) * [None]) # fill gap with None
        self.append(value) # append new value
        return value # copy return behaviour

>>> a = MyList()
>>> a[0] = 1
>>> a[2] = 1
>>> (a, a[3])
([1, None, 1], None)
>>> (a.length, a['length'])
(3, 3)

Answer 3

我想不出这是实现的本地方式。说到这一点，创建一个能达到预期效果的功能并不是一个坏主意。您可以使用以下内容代替使用my_list[index] = value：

def insertWithAutoFill(the_list, index, new_item):
    if index >= len(the_list):
        for i in range(len(the_list), index):
             the_list.append(None)
        the_list.append(new_item)
    else:
        the_list[index] = new_item

你会这样称呼：

my_list = [1, 2, 3]
insertWithAutoFill(my_list, 6, 23)

现在my_list包含：

[1, 2, 3, None, None, None, 23]

您可能需要调整一些内容以确保正确检查某些内容并正确使用index。这是在特定情况下进行了轻微测试和工作，但并不能保证完美：）

用Python模拟JavaScript数组

3 个答案: