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\'

Answer 1

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.

Answer 2

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%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 )

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%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 )

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:

1. Python: How to generate the code on the fly?
2. https://en.wikipedia.org/wiki/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.

Answer 3

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.

Answer 4

Try destination.__dict__.update(source.__dict__).

Answer 5

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.