python - 实现 copy.deepcopy() 克隆函数

Question

仅用于教育目的，我正在尝试实现 copy.deepcopy() 的克隆功能。

在玩代码和谷歌搜索之后，我想出了以下函数:

def my_deepcopy(data):

    if isinstance(data, dict):
        result = {}
        for key, value in data.items():
            result[key] = my_deepcopy(value)

        assert id(result) != id(data)

    elif isinstance(data, list):
        result = []
        for item in data:
            result.append(my_deepcopy(item))

        assert id(result) != id(data)

    elif isinstance(data, tuple):
        aux = []
        for item in data:
            aux.append(my_deepcopy(item))
        result = tuple(aux)

        assert id(result) != id(data)

    elif isinstance(data, (int, float, type(None), str, bool)):
        result = data
    else:
        raise ValueError("unexpected type")

    return result

它似乎适用于所有 Python 基本类型及其组合:

# Various object types
lst_obj = [ 0, 1.1, 'foo', 'bar' ]
dict_obj = { 'zero' : 0, 'pi' : 3.1415, 'desc' : 'foobar' }
list_list_obj = [ [1,2,3], [4,5,6], [7,8,9] ]
tuple_list_obj = [ (-1,-1), (0,-1,0), (-1,0), (0,0,0,0) ]
dict_list_obj = [ {'zero' : 0}, {'pi' : 3.1415}, {'desc' : 'foobar'} ]

# Testing
my_deepcopy( lst_obj )        #OK!
my_deepcopy( dict_obj )       #OK!
my_deepcopy( list_list_obj )  #OK!
my_deepcopy( tuple_list_obj ) #OK!
my_deepcopy( dict_list_obj )  #OK!

到目前为止，还不错，但是 Arbitrary Types 呢？如何复制任意对象的实例？我如何检测它？任意类型是否有任何类型的复制构造函数？

为了使以下代码正常工作，我的函数中缺少什么:

class Xpto:
    pass

arbitrary = [ Xpto(), Xpto() ]
my_deepcopy( arbitrary )     #ValueError("unexpected type")

Answer 1

你可以做一些“类别检查”来更好地设计你的函数，通过任意对象的 __dict__ 属性搜索序列或映射:

>>> import collections
>>> isinstance([], collections.Sequence)
True
>>> isinstance((), collections.Sequence)
True
>>> isinstance('foo', collections.Sequence)
True
>>> isinstance({}, collections.Mapping)
True
>>> isinstance(23, collections.Sequence)
False
>>> isinstance(None, collections.Sequence)
False

还要检查 __class__ 或 __name__ 属性，以检查对象是否从某个不在您的 if 语句中的类类型实例化，例如:

def my_deepcopy(data):

    if isinstance(data, dict):
        result = {}
        for key, value in data.items():

            result[key] = my_deepcopy(value)

        assert id(result) != id(data)

    elif isinstance(data, list):
        result = []
        for item in data:
            result.append(my_deepcopy(item))

        assert id(result) != id(data)

    elif isinstance(data, tuple):
        aux = []
        for item in data:
            aux.append(my_deepcopy(item))
        result = tuple(aux)

        assert id(result) != id(data)

    elif isinstance(data, (int, float, type(None), str, bool)):
        result = data

    elif hasattr(data, '__name__'):#Its a function or a class
        auxObj = data.__class__() #Assuming it has not __init__ method defined
        auxDict = {}
        for key, value in data.__dict__:
            auxDict[key] = my_deepcopy(value)

        assert id(result) != id(data)

    else:
        raise ValueError("unexpected type")

    return result