Is there anything that pickle + copy_reg cannot serialize?

[Maurice LING]

>>> Since copy_reg lets you specify arbitrary code to serialize arbitrary
>>> objects, you shouldn't run into any single object that you cannot
>>> serialize to a pickle.
>>
>>
>> [snip - example of pickling code objects]
>>
>>
>> I cannot understand 2 things, which I seek assistance for:
>> 1. Is code object the only thing can cannot be pickled (less facing
>> recursion limits)?
> 
> 
> No.  There are lots of objects that cannot be pickled by default.  Any 
> extension type which does not explicitly support it cannot be pickled.  
> Generators cannot be pickled.  Method descriptors can't be pickled.  Et 
> cetera.

Thank Jean-Paul.

Sorry for not specifying clearly enough. Given that copy_reg lets you 
specify arbitrary code to serialize arbitrary objects, of which some are 
taken care of by pickle, in the set of possible Python types,

 >>> import types
 >>> dir(types)
['BooleanType', 'BufferType', 'BuiltinFunctionType', 
'BuiltinMethodType', 'ClassType', 'CodeType', 'ComplexType', 
'DictProxyType', 'DictType', 'DictionaryType', 'EllipsisType', 
'FileType', 'FloatType', 'FrameType', 'FunctionType', 'GeneratorType', 
'InstanceType', 'IntType', 'LambdaType', 'ListType', 'LongType', 
'MethodType', 'ModuleType', 'NoneType', 'NotImplementedType', 
'ObjectType', 'SliceType', 'StringType', 'StringTypes', 'TracebackType', 
'TupleType', 'TypeType', 'UnboundMethodType', 'UnicodeType', 
'XRangeType', '__builtins__', '__doc__', '__file__', '__name__']

What types cannot be serialized by pickle (besides CodeType) and 
requires handling using copy_reg?

Thanks
Maurice


> 
>> 2. In the above example, how copy_reg works with pickle?
> 
> 
> Any time pickle thinks it has found something it cannot pickle, it asks 
> the copy_reg module for some help.  The above example basically teaches 
> the copy_reg module how to give the pickle module the help it needs for 
> code objects.
> 
> Jean-Paul