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如何在Python中将对象的所有属性复制到另一个对象?

python

Joril · 技术社区 · 16 年前

在Python中,是否有一个库方法来复制同一类的两个(已经存在的)实例之间的所有属性?

我是说,有点像阿帕奇公地 PropertyUtilsBean.copyProperties()

6 回复 | 直到 6 年前

ArtOfWarfare 9 年前

如果你的类不修改 __getitem__ 或 __setitem__ 对于特殊属性访问,所有属性都存储在 __dict__ 所以你可以这样做:

 nobj.__dict__ = oobj.__dict__.copy()    # just a shallow copy

如果您使用python属性,您应该看看 inspect.getmembers() 过滤掉你想要复制的。

Peter Hosey 16 年前

尝试 destination.__dict__.update(source.__dict__) .

J S 16 年前

我知道你抄袭了,但我不同意。制作另一个副本比用 双关语 如其他人建议的那样,操作(如果通过重新分配变量而丢失现有副本,则会立即对其进行垃圾收集)。python并不意味着要快,而是要可读(尽管我实际上相信copy()比其他方法更快)。

Ali Afshar 16 年前

如果必须这样做,我想最好的方法是使用类属性,比如:

Class Copyable(object):
    copyable_attributes = ('an_attribute', 'another_attribute')

然后显式地迭代它们并使用 setattr(new, attr, getattr(old, attr)) . 不过,我仍然相信用更好的设计可以解决问题,而且不推荐这样做。

Ali Afshar 16 年前

冒着被改造的危险,有没有 ~~像样的~~ 有这个的用例吗?

除非我们确切地知道它是用来干什么的,否则我们不能明智地把它称为“坏的”,就像它看起来的那样。

也许可以试试这个:

firstobject.an_attribute = secondobject.an_attribute
firstobject.another_attribute = secondobject.another_attribute

这是在实例之间复制东西的明智方法。

Evandro Coan 7 年前

使用此功能,您几乎可以将所有内容从一个对象复制到另一个对象:

import sys

_target_object = sys.stderr
_target_object_class_type = type( _target_object )

class TargetCopiedObject(_target_object_class_type):
    """
        Which special methods bypasses __getattribute__ in Python?
        https://stackoverflow.com/questions/12872695/which-special-methods-bypasses
    """

    if hasattr( _target_object, "__abstractmethods__" ):
        __abstractmethods__ = _target_object.__abstractmethods__

    if hasattr( _target_object, "__base__" ):
        __base__ = _target_object.__base__

    if hasattr( _target_object, "__bases__" ):
        __bases__ = _target_object.__bases__

    if hasattr( _target_object, "__basicsize__" ):
        __basicsize__ = _target_object.__basicsize__

    if hasattr( _target_object, "__call__" ):
        __call__ = _target_object.__call__

    if hasattr( _target_object, "__class__" ):
        __class__ = _target_object.__class__

    if hasattr( _target_object, "__delattr__" ):
        __delattr__ = _target_object.__delattr__

    if hasattr( _target_object, "__dict__" ):
        __dict__ = _target_object.__dict__

    if hasattr( _target_object, "__dictoffset__" ):
        __dictoffset__ = _target_object.__dictoffset__

    if hasattr( _target_object, "__dir__" ):
        __dir__ = _target_object.__dir__

    if hasattr( _target_object, "__doc__" ):
        __doc__ = _target_object.__doc__

    if hasattr( _target_object, "__eq__" ):
        __eq__ = _target_object.__eq__

    if hasattr( _target_object, "__flags__" ):
        __flags__ = _target_object.__flags__

    if hasattr( _target_object, "__format__" ):
        __format__ = _target_object.__format__

    if hasattr( _target_object, "__ge__" ):
        __ge__ = _target_object.__ge__

    if hasattr( _target_object, "__getattribute__" ):
        __getattribute__ = _target_object.__getattribute__

    if hasattr( _target_object, "__gt__" ):
        __gt__ = _target_object.__gt__

    if hasattr( _target_object, "__hash__" ):
        __hash__ = _target_object.__hash__

    if hasattr( _target_object, "__init__" ):
        __init__ = _target_object.__init__

    if hasattr( _target_object, "__init_subclass__" ):
        __init_subclass__ = _target_object.__init_subclass__

    if hasattr( _target_object, "__instancecheck__" ):
        __instancecheck__ = _target_object.__instancecheck__

    if hasattr( _target_object, "__itemsize__" ):
        __itemsize__ = _target_object.__itemsize__

    if hasattr( _target_object, "__le__" ):
        __le__ = _target_object.__le__

    if hasattr( _target_object, "__lt__" ):
        __lt__ = _target_object.__lt__

    if hasattr( _target_object, "__module__" ):
        __module__ = _target_object.__module__

    if hasattr( _target_object, "__mro__" ):
        __mro__ = _target_object.__mro__

    if hasattr( _target_object, "__name__" ):
        __name__ = _target_object.__name__

    if hasattr( _target_object, "__ne__" ):
        __ne__ = _target_object.__ne__

    if hasattr( _target_object, "__new__" ):
        __new__ = _target_object.__new__

    if hasattr( _target_object, "__prepare__" ):
        __prepare__ = _target_object.__prepare__

    if hasattr( _target_object, "__qualname__" ):
        __qualname__ = _target_object.__qualname__

    if hasattr( _target_object, "__reduce__" ):
        __reduce__ = _target_object.__reduce__

    if hasattr( _target_object, "__reduce_ex__" ):
        __reduce_ex__ = _target_object.__reduce_ex__

    if hasattr( _target_object, "__repr__" ):
        __repr__ = _target_object.__repr__

    if hasattr( _target_object, "__setattr__" ):
        __setattr__ = _target_object.__setattr__

    if hasattr( _target_object, "__sizeof__" ):
        __sizeof__ = _target_object.__sizeof__

    if hasattr( _target_object, "__str__" ):
        __str__ = _target_object.__str__

    if hasattr( _target_object, "__subclasscheck__" ):
        __subclasscheck__ = _target_object.__subclasscheck__

    if hasattr( _target_object, "__subclasses__" ):
        __subclasses__ = _target_object.__subclasses__

    if hasattr( _target_object, "__subclasshook__" ):
        __subclasshook__ = _target_object.__subclasshook__

    if hasattr( _target_object, "__text_signature__" ):
        __text_signature__ = _target_object.__text_signature__

    if hasattr( _target_object, "__weakrefoffset__" ):
        __weakrefoffset__ = _target_object.__weakrefoffset__

    if hasattr( _target_object, "mro" ):
        mro = _target_object.mro

    def __init__(self):
        """
            Override any super class `type( _target_object )` constructor,
            so we can instantiate any kind of replacement object.

            Assures all properties were statically replaced just above. This
            should happen in case some new attribute is added to the python
            language.

            This also ignores the only two methods which are not equal,
            `__init__()` and `__getattribute__()`.

            How do you programmatically set an attribute?
            https://stackoverflow.com/questions/285061/how-do-you-programmatically
        """
        different_methods = set(["__init__", "__getattribute__"])
        attributes_to_check = set( dir( object ) + dir( type ) )
        attributes_to_copy = dir( _target_object )

        # Check for missing magic built-ins methods on the class static initialization
        for attribute in attributes_to_check:

            if attribute not in different_methods \
                    and hasattr( _target_object, attribute ):

                base_class_attribute = self.__getattribute__( attribute )
                target_class_attribute = _target_object.__getattribute__( attribute )

                if base_class_attribute != target_class_attribute:
                    sys.stdout.write(
                            "    The base class attribute `%s` is different from the "
                            "target class:\n%s\n%s\n\n" % ( attribute,
                                                    base_class_attribute, 
                                                    target_class_attribute ) )
        # Finally copy everything it can
        different_methods.update( attributes_to_check )

        for attribute in attributes_to_copy:

            if attribute not in different_methods:
                print( "Setting:", attribute )

                try:
                    target_class_attribute = _target_object.__getattribute__(attribute)
                    setattr( self, attribute, target_class_attribute )

                except AttributeError as error:
                    print( "Error coping the attribute `%s`: %s" % (attribute, error) )


o = TargetCopiedObject()
print( "TargetCopiedObject:", o )

但是,如果运行上面的代码,您将看到以下错误:

python test.py
Setting: _CHUNK_SIZE
Setting: __del__
Setting: __enter__
Setting: __exit__
Setting: __getstate__
Setting: __iter__
Setting: __next__
Setting: _checkClosed
Setting: _checkReadable
Setting: _checkSeekable
Setting: _checkWritable
Setting: _finalizing
Setting: buffer
Error coping the attribute `buffer`: readonly attribute
Setting: close
Setting: closed
Error coping the attribute `closed`: attribute 'closed' of '_io.TextIOWrapper' objects is not writable
Setting: detach
Setting: encoding
Error coping the attribute `encoding`: readonly attribute
Setting: errors
Error coping the attribute `errors`: attribute 'errors' of '_io.TextIOWrapper' objects is not writable
Setting: fileno
Setting: flush
Setting: isatty
Setting: line_buffering
Error coping the attribute `line_buffering`: readonly attribute
Setting: mode
Setting: name
Error coping the attribute `name`: attribute 'name' of '_io.TextIOWrapper' objects is not writable
Setting: newlines
Error coping the attribute `newlines`: attribute 'newlines' of '_io.TextIOWrapper' objects is not writable
Setting: read
Setting: readable
Setting: readline
Setting: readlines
Setting: seek
Setting: seekable
Setting: tell
Setting: truncate
Setting: writable
Setting: write
Setting: writelines
TargetCopiedObject: <_io.TextIOWrapper name='<stderr>' mode='w' encoding='utf-8'>

您只能通过在类静态初始化上执行这些只读属性,就像其他内置的magic python方法一样 __str__ 正上方:

import sys

_target_object = sys.stderr
_target_object_class_type = type( _target_object )

class TargetCopiedObject(_target_object_class_type):
    """
        Which special methods bypasses __getattribute__ in Python?
        https://stackoverflow.com/questions/12872695/which-special-methods-bypasses
    """

    if hasattr( _target_object, "__abstractmethods__" ):
        __abstractmethods__ = _target_object.__abstractmethods__

    if hasattr( _target_object, "__base__" ):
        __base__ = _target_object.__base__

    if hasattr( _target_object, "__bases__" ):
        __bases__ = _target_object.__bases__

    if hasattr( _target_object, "__basicsize__" ):
        __basicsize__ = _target_object.__basicsize__

    if hasattr( _target_object, "__call__" ):
        __call__ = _target_object.__call__

    if hasattr( _target_object, "__class__" ):
        __class__ = _target_object.__class__

    if hasattr( _target_object, "__delattr__" ):
        __delattr__ = _target_object.__delattr__

    if hasattr( _target_object, "__dict__" ):
        __dict__ = _target_object.__dict__

    if hasattr( _target_object, "__dictoffset__" ):
        __dictoffset__ = _target_object.__dictoffset__

    if hasattr( _target_object, "__dir__" ):
        __dir__ = _target_object.__dir__

    if hasattr( _target_object, "__doc__" ):
        __doc__ = _target_object.__doc__

    if hasattr( _target_object, "__eq__" ):
        __eq__ = _target_object.__eq__

    if hasattr( _target_object, "__flags__" ):
        __flags__ = _target_object.__flags__

    if hasattr( _target_object, "__format__" ):
        __format__ = _target_object.__format__

    if hasattr( _target_object, "__ge__" ):
        __ge__ = _target_object.__ge__

    if hasattr( _target_object, "__getattribute__" ):
        __getattribute__ = _target_object.__getattribute__

    if hasattr( _target_object, "__gt__" ):
        __gt__ = _target_object.__gt__

    if hasattr( _target_object, "__hash__" ):
        __hash__ = _target_object.__hash__

    if hasattr( _target_object, "__init__" ):
        __init__ = _target_object.__init__

    if hasattr( _target_object, "__init_subclass__" ):
        __init_subclass__ = _target_object.__init_subclass__

    if hasattr( _target_object, "__instancecheck__" ):
        __instancecheck__ = _target_object.__instancecheck__

    if hasattr( _target_object, "__itemsize__" ):
        __itemsize__ = _target_object.__itemsize__

    if hasattr( _target_object, "__le__" ):
        __le__ = _target_object.__le__

    if hasattr( _target_object, "__lt__" ):
        __lt__ = _target_object.__lt__

    if hasattr( _target_object, "__module__" ):
        __module__ = _target_object.__module__

    if hasattr( _target_object, "__mro__" ):
        __mro__ = _target_object.__mro__

    if hasattr( _target_object, "__name__" ):
        __name__ = _target_object.__name__

    if hasattr( _target_object, "__ne__" ):
        __ne__ = _target_object.__ne__

    if hasattr( _target_object, "__new__" ):
        __new__ = _target_object.__new__

    if hasattr( _target_object, "__prepare__" ):
        __prepare__ = _target_object.__prepare__

    if hasattr( _target_object, "__qualname__" ):
        __qualname__ = _target_object.__qualname__

    if hasattr( _target_object, "__reduce__" ):
        __reduce__ = _target_object.__reduce__

    if hasattr( _target_object, "__reduce_ex__" ):
        __reduce_ex__ = _target_object.__reduce_ex__

    if hasattr( _target_object, "__repr__" ):
        __repr__ = _target_object.__repr__

    if hasattr( _target_object, "__setattr__" ):
        __setattr__ = _target_object.__setattr__

    if hasattr( _target_object, "__sizeof__" ):
        __sizeof__ = _target_object.__sizeof__

    if hasattr( _target_object, "__str__" ):
        __str__ = _target_object.__str__

    if hasattr( _target_object, "__subclasscheck__" ):
        __subclasscheck__ = _target_object.__subclasscheck__

    if hasattr( _target_object, "__subclasses__" ):
        __subclasses__ = _target_object.__subclasses__

    if hasattr( _target_object, "__subclasshook__" ):
        __subclasshook__ = _target_object.__subclasshook__

    if hasattr( _target_object, "__text_signature__" ):
        __text_signature__ = _target_object.__text_signature__

    if hasattr( _target_object, "__weakrefoffset__" ):
        __weakrefoffset__ = _target_object.__weakrefoffset__

    if hasattr( _target_object, "mro" ):
        mro = _target_object.mro

    # Copy all the other read only attributes
    if hasattr( _target_object, "buffer" ):
        buffer = _target_object.buffer

    if hasattr( _target_object, "closed" ):
        closed = _target_object.closed

    if hasattr( _target_object, "encoding" ):
        encoding = _target_object.encoding

    if hasattr( _target_object, "errors" ):
        errors = _target_object.errors

    if hasattr( _target_object, "line_buffering" ):
        line_buffering = _target_object.line_buffering

    if hasattr( _target_object, "name" ):
        name = _target_object.name

    if hasattr( _target_object, "newlines" ):
        newlines = _target_object.newlines

    def __init__(self):
        """
            Override any super class `type( _target_object )` constructor,
            so we can instantiate any kind of replacement object.

            Assures all properties were statically replaced just above. This
            should happen in case some new attribute is added to the python
            language.

            This also ignores the only two methods which are not equal,
            `__init__()` and `__getattribute__()`.

            How do you programmatically set an attribute?
            https://stackoverflow.com/questions/285061/how-do-you-programmatically
        """

        # Add the copied read only atribute to the ignored list, so they
        # do not throw new errors while trying copy they dynamically
        different_methods = set\
        ([
            "__init__",
            "__getattribute__",
            "buffer",
            "closed",
            "encoding",
            "errors",
            "line_buffering",
            "name",
            "newlines",
        ])

        attributes_to_check = set( dir( object ) + dir( type ) )
        attributes_to_copy = dir( _target_object )

        # Check for missing magic built-ins methods on the class static initialization
        for attribute in attributes_to_check:

            if attribute not in different_methods \
                    and hasattr( _target_object, attribute ):

                base_class_attribute = self.__getattribute__( attribute )
                target_class_attribute = _target_object.__getattribute__( attribute )

                if base_class_attribute != target_class_attribute:
                    sys.stdout.write(
                            "    The base class attribute `%s` is different from the "
                            "target class:\n%s\n%s\n\n" % ( attribute,
                                                    base_class_attribute,
                                                    target_class_attribute ) )
        # Finally copy everything it can
        different_methods.update( attributes_to_check )

        for attribute in attributes_to_copy:

            if attribute not in different_methods:
                print( "Setting:", attribute )

                try:
                    target_class_attribute = _target_object.__getattribute__(attribute)
                    setattr( self, attribute, target_class_attribute )

                except AttributeError as error:
                    print( "Error coping the attribute `%s`: %s" % (attribute, error) )


o = TargetCopiedObject()
print( "TargetCopiedObject:", o )

现在,这个新版本完全可以处理所有问题:

python test.py
Setting: _CHUNK_SIZE
Setting: __del__
Setting: __enter__
Setting: __exit__
Setting: __getstate__
Setting: __iter__
Setting: __next__
Setting: _checkClosed
Setting: _checkReadable
Setting: _checkSeekable
Setting: _checkWritable
Setting: _finalizing
Setting: close
Setting: detach
Setting: fileno
Setting: flush
Setting: isatty
Setting: mode
Setting: read
Setting: readable
Setting: readline
Setting: readlines
Setting: seek
Setting: seekable
Setting: tell
Setting: truncate
Setting: writable
Setting: write
Setting: writelines
TargetCopiedObject: <_io.TextIOWrapper name='<stderr>' mode='w' encoding='utf-8'>

它的缺点是需要手动编写Python代码来克服只读属性。但是,您可以使用元编程即时编写python代码:

因此,如果您处理上面的初始代码,您可以编写一个脚本来生成它需要的代码。因此,您可以动态地完全复制任何Python对象。