如何在Python中将对象的所有属性复制到另一个对象?

时间:2008-10-28 15:58:11

标签: python

是否有一种库方法可以在Python中复制同一类的两个(已存在的)实例之间的所有属性?

我的意思是,像Apache Commons'PropertyUtilsBean.copyProperties()

5 个答案:

答案 0 :(得分:53)

尝试destination.__dict__.update(source.__dict__)

答案 1 :(得分:35)

如果您的班级没有修改__getitem____setitem__进行特殊属性访问,则所有属性都会存储在__dict__中,以便您可以这样做:

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

如果使用python属性,则应查看inspect.getmembers()并过滤掉要复制的属性。

答案 2 :(得分:2)

如果你必须这样做,我想最好的方法是有一个类属性:

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

然后显式迭代它们并使用setattr(new, attr, getattr(old, attr))。我仍然相信它可以用更好的设计解决,但不推荐它。

答案 3 :(得分:1)

冒被压缩的风险,是否适合任何用例?

除非我们确切知道它的用途,否则我们无法将其视为“破碎”。

也许试试这个:

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

这是在实例之间复制事物的理智方式。

答案 4 :(得分:0)

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,如果您运行上面的代码,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'>

您只能通过类静态初始化来复制这些只读属性,就像上面的__str__中的其他内置魔术python方法一样:

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解决所有问题:

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'>

它的缺点是你需要手动编写Python代码来克服只读属性。但是,您可以使用元编程动态编写python代码:

  1. Python: How to generate the code on the fly?
  2. https://en.wikipedia.org/wiki/Metaprogramming
  3. 因此,如果你在上面编写这个初始代码,你可以编写一个生成所需代码的脚本。因此,您可以动态完全复制任何Python对象。