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()
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__或__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：
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。