Adding support for serializing datetime.datetime instances

[jreyesr]

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]

Hi, I'm glad you like Streamsync!

As you mentioned, datetime.datetime cannot be serialised because there's no code that can handle it.

This would be easy to implement and definitely useful, so I'll open an issue.

Thanks for suggesting this.

[jreyesr]

For cleanup, this was resolved in #41