On 02.12.2015 20:16, Serhiy Storchaka wrote:
> 
> Serhiy Storchaka added the comment:
> 
>> If the StreamWriter/Reader cannot pickle the underlying stream (which is
>> probably always the case), why should the object itself be pickleable ?
> 
> io.BytesIO() and io.StringIO() are pickleable.

Ok, but I still don't see the use case :-)

I think all we need to do is add a .__reduce__()
method to StreamWriter and StreamReader, which then
raises a PickleError.

Example:

>>> import sys, codecs, pickle
>>> r = codecs.getreader('latin-1')
>>> class MyReader(r):
...    def __reduce__(self, *args):
...       raise pickle.PickleError
...
>>> s = MyReader(sys.stdin)
>>> pickle.dumps(s)
Traceback (most recent call last):
  File "<stdin>", line 1, in <module>
  File "<stdin>", line 3, in __reduce__
_pickle.PickleError
> <stdin>(3)__reduce__()