How to copy all properties of an object to another object, in Python?
Question:
Is there a library method to copy all the properties between two (already present) instances of the same class, in Python?
I mean, something like Apache Commons’ PropertyUtilsBean.copyProperties()
Answers:
If your class does not modify __getitem__ or __setitem__ for special attribute access all your attributes are stored in __dict__ so you can do:
nobj.__dict__ = oobj.__dict__.copy() # just a shallow copy
If you use python properties you should look at inspect.getmembers() and filter out the ones you want to copy.
Try destination.__dict__.update(source.__dict__).
At the risk of being modded down, is there a decent any use-case for this?
Unless we know exactly what it’s for, we can’t sensibly call it as “broken” as it seems.
Perhaps try this:
firstobject.an_attribute = secondobject.an_attribute
firstobject.another_attribute = secondobject.another_attribute
That’s the sane way of copying things between instances.
If you have to do this, I guess the nicest way is to have a class attribute something like :
Class Copyable(object):
copyable_attributes = ('an_attribute', 'another_attribute')
Then iterate them explicitly and use setattr(new, attr, getattr(old, attr)). I still believe it can be solved with a better design though, and don’t recommend it.
Using this you can almost copy everything from one object to another:
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%sn%snn" % ( 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 )
However, if you run the code above, you will see these errors:
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'>
You can only copy these read-only properties by doing it on the class static initialization, like the other built-in magic python methods as __str__ just above:
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%sn%snn" % ( 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 )
Now this new version completely works coping everything:
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'>
The disadvantage of it is that you need to write the Python code manually to overcome the read only attributes. However, you can write python code on the fly with metaprogramming:
So, if you work over this initial code just above, you can write a script which generates the code it needs to. Hence, you can dynamically and completely copy any Python object.
For class objects, I find it’s best to add their own copy method. This allows a work around for internal, non-pickelable objects in the deepcopy:
import copy
class Foo:
def __init__(self):
self._var1 = 'foo'
self._var2 = 'goo'
...
def __copy__(self):
new_obj = self.__class__()
for k,v in vars(self).items():
try:
setattr(new_obj, k, copy.deepcopy(v))
except:
pass # non-pickelable stuff wasn't needed
return new_obj
def copy(self):
return self.__copy__()
...
In your working code, it would then become:
a = Foo()
b = a.copy()
This is a toy problem of course. In reality, you would do this if you have complex objects within your class which cannot be readily copied directly with the copy.deepcopy() type operation. If it were a simple problem, just use b = copy.deepcopy(a) without the explicit definition in the class.
Is there a library method to copy all the properties between two (already present) instances of the same class, in Python?
I mean, something like Apache Commons’ PropertyUtilsBean.copyProperties()
If your class does not modify __getitem__ or __setitem__ for special attribute access all your attributes are stored in __dict__ so you can do:
nobj.__dict__ = oobj.__dict__.copy() # just a shallow copy
If you use python properties you should look at inspect.getmembers() and filter out the ones you want to copy.
Try destination.__dict__.update(source.__dict__).
At the risk of being modded down, is there a decent any use-case for this?
Unless we know exactly what it’s for, we can’t sensibly call it as “broken” as it seems.
Perhaps try this:
firstobject.an_attribute = secondobject.an_attribute
firstobject.another_attribute = secondobject.another_attribute
That’s the sane way of copying things between instances.
If you have to do this, I guess the nicest way is to have a class attribute something like :
Class Copyable(object):
copyable_attributes = ('an_attribute', 'another_attribute')
Then iterate them explicitly and use setattr(new, attr, getattr(old, attr)). I still believe it can be solved with a better design though, and don’t recommend it.
Using this you can almost copy everything from one object to another:
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%sn%snn" % ( 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 )
However, if you run the code above, you will see these errors:
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'>
You can only copy these read-only properties by doing it on the class static initialization, like the other built-in magic python methods as __str__ just above:
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%sn%snn" % ( 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 )
Now this new version completely works coping everything:
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'>
The disadvantage of it is that you need to write the Python code manually to overcome the read only attributes. However, you can write python code on the fly with metaprogramming:
So, if you work over this initial code just above, you can write a script which generates the code it needs to. Hence, you can dynamically and completely copy any Python object.
For class objects, I find it’s best to add their own copy method. This allows a work around for internal, non-pickelable objects in the deepcopy:
import copy
class Foo:
def __init__(self):
self._var1 = 'foo'
self._var2 = 'goo'
...
def __copy__(self):
new_obj = self.__class__()
for k,v in vars(self).items():
try:
setattr(new_obj, k, copy.deepcopy(v))
except:
pass # non-pickelable stuff wasn't needed
return new_obj
def copy(self):
return self.__copy__()
...
In your working code, it would then become:
a = Foo()
b = a.copy()
This is a toy problem of course. In reality, you would do this if you have complex objects within your class which cannot be readily copied directly with the copy.deepcopy() type operation. If it were a simple problem, just use b = copy.deepcopy(a) without the explicit definition in the class.