DOC: Serialization recommendation is deprecated

[chrisroat]

Location of the documentation

https://pandas.pydata.org/pandas-docs/dev/user_guide/io.html#io-msgpack

Documentation problem

Since the deprecation of msgpack for on-the-wire transmission, it is recommended to use pyarrow serialization/deserialization. However, since pyarrow 2.0, this has been deprecated for arbitrary objects. A deprecation message is emitted when using the documented code snippet.

$ python
Python 3.8.5 (default, Jul 28 2020, 12:59:40) 
[GCC 9.3.0] on linux
Type "help", "copyright", "credits" or "license" for more information.
>>> import pyarrow as pa
>>> pa.__version__
'3.0.0'
>>> pa.default_serialization_context()
<stdin>:1: DeprecationWarning: 'pyarrow.default_serialization_context' is deprecated as of 2.0.0 and will be removed in a future version. Use pickle or the pyarrow IPC functionality instead.
<pyarrow.lib.SerializationContext object at 0x7f23dfa36940>
>>> 

Suggested fix for documentation

Would pickle be next in line for a recommended on-the-wire format?

[jreback]

no just need to update to the renamed pyarrow format

[chrisroat]

I may not understand the situation fully -- what is renamed? The deprecation message in the pyarrow docs linked above recommends pickle for non-pyarrow objects. One can convert a dataframe to/from pyarrow table, but it may not be fully compatible.

[jorisvandenbossche]

@chrisroat thanks for the report! We should indeed have updated our docs after pyarrow deprecated the serialization functionality.

The most appropriate alternative will depend on your exact use case, but in general I think we can indeed refer users to use pickle instead.

[simonjayhawkins]

removing 1.3 milestone.

[jorisvandenbossche]

It's important to fix this, as our docs are simply pointing to a (soon) no-longer existing alternative. Since this is arrow-related, will look into it one of the next days (not crucial for the RC of course)