分配时列表的 Python 深度复制

发布于 2025-01-08 11:06:01 字数 722 浏览 3 评论 0原文

在 python 考试中得到了这个练习。尝试返回一个列表的深层副本，如下所示：

l = list()
l = [0,1,2]
l1 = l
l[0] = 1

l1 should contains [0,1,2] not [1,1,2]

指定要实现的练习通过使用元类来实现。

class deep(type):
    def __new__(meta, classname, bases, classDict):
        return type.__new__(meta, classname, bases, classDict)
    def __init__(cls, name, bases, dct):
        super(deep, cls).__init__(name, bases, dct)
    def __call__(cls, *args, **kwds):
        return type.__call__(cls, *args, **kwds)            
class list(metaclass=deep):
    def __init__(self):
        pass

据我所知，python中的'='是一个语句而不是一个运算符，它不能被覆盖。关于如何在作业中返回深层副本有什么想法吗？已经尝试了很多但没有成功。

原文

Got this exercise on a python exam.
Trying to return a deep o copy of a list like this:

l = list()
l = [0,1,2]
l1 = l
l[0] = 1

l1 should contain [0,1,2] not [1,1,2]

The exercise specified to implement it by using a metaclass.

class deep(type):
    def __new__(meta, classname, bases, classDict):
        return type.__new__(meta, classname, bases, classDict)
    def __init__(cls, name, bases, dct):
        super(deep, cls).__init__(name, bases, dct)
    def __call__(cls, *args, **kwds):
        return type.__call__(cls, *args, **kwds)            
class list(metaclass=deep):
    def __init__(self):
        pass

From what i know , the '=' in python is a statement and not an operator and it can't be overriden. Any idea on how to return a deep copy on assignment? Have been trying quite a lot but with no success.

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十六岁半 2025-01-15 11:06:01

据我所知，如果不使用某种额外的语法，这在 python 中是不可能的。正如您所说，您无法覆盖 =。

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森林迷了鹿 2025-01-15 11:06:01

要了解 l1 = l 在 Python 中的作用，请阅读其他语言有“变量”，Python有“名称”。

要更改 l[0] = 1 的功能，您可以重写 l 的 __setitem__() 方法：

>>> class L(list):
...     def __setitem__(self, i, v):
...         list.__setitem__(self, i, 10)
... 
>>> l = L()
>>> l.append(1)
>>> l
[1]
>>> l[0] = 0
>>> l
[10]

要更改 l = 的内容列表（）; l = [0,1,2] 您可以在 CPython 中定义 List.__del__() 方法并操作 l 所属的命名空间，例如使用 <代码>检查模块。不用说，你永远不应该这样做。

>>> import inspect
>>> class L:
...     def __del__(self):
...         inspect.currentframe().f_globals['l'] = [1,2,3]
... 
>>> l = L()
>>> l = [0]
>>> l
[1, 2, 3]

To understand what l1 = l does in Python read Other languages have "variables", Python has "names".

To change what l[0] = 1 does you could override l's __setitem__() method:

>>> class L(list):
...     def __setitem__(self, i, v):
...         list.__setitem__(self, i, 10)
... 
>>> l = L()
>>> l.append(1)
>>> l
[1]
>>> l[0] = 0
>>> l
[10]

To change what l = List(); l = [0,1,2] does you could define List.__del__() method in CPython and manipulate the namespace l belongs to e.g., using inspect module. Needless to say you should never do that.

>>> import inspect
>>> class L:
...     def __del__(self):
...         inspect.currentframe().f_globals['l'] = [1,2,3]
... 
>>> l = L()
>>> l = [0]
>>> l
[1, 2, 3]

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