Adding support for serializing datetime.datetime instances

[ramedina86]

Discussed in #40

^{Originally posted by jreyesr June 17, 2023}
Hello! I've been exploring Streamsync (awesome tool, BTW!) and I found out that apparently datetime.datetime instances cannot be serialized and sent to the frontend.

Minimal example

import datetime
import streamsync as ss

initial_state = ss.init_state({
  "now": datetime.datetime.now(),
})

This causes the following error to appear:

Error

Serialisation error

Traceback (most recent call last):
  File "/home/reyes/.local/lib/python3.10/site-packages/streamsync/core.py", line 239, in to_dict
    serialised_value = state_serialiser.serialise(value)
  File "/home/reyes/.local/lib/python3.10/site-packages/streamsync/core.py", line 129, in serialise
    raise StateSerialiserException(
streamsync.core.StateSerialiserException: Object of type <class 'datetime.datetime'> (MRO: ['datetime.datetime', 'datetime.date', 'builtins.object']) cannot be serialised.

During handling of the above exception, another exception occurred:

Traceback (most recent call last):
  File "/home/reyes/.local/lib/python3.10/site-packages/streamsync/app_runner.py", line 120, in _handle_session_init
    user_state = session.session_state.user_state.to_dict()
  File "/home/reyes/.local/lib/python3.10/site-packages/streamsync/core.py", line 241, in to_dict
    raise ValueError(
ValueError: Couldn't serialise value of type "<class 'datetime.datetime'>" for key "now".

As far as I can tell, this is due to the serialization code not supporting datetime.datetime instances

Background: I ran across this when trying to replicate Streamlit's starter tutorial in Streamsync. This tutorial has a Pandas DataFrame with a datetime column (it's a special Pandas datetime class, but it eventually inherits from Python's datetime.datetime)

Adding support for this would let users display data that has timestamp-style columns, such as "created on", "event time" and such.

Is there any interest in letting users pass datetime instances to the FE? I don't see any issues or discussions mentioning it, but it may be because Streamsync is fairly new. Any ideas?

[ramedina86]

datetime.datetime is now serialisable in 0.1.9.