A possible design for doing per-session persistent state in Streamlit

SessionState.py

# https://gist.github.com/FranzDiebold/898396a6be785d9b5ca6f3706ef9b0bc
"""Hack to add per-session state to Streamlit.

Works for Streamlit >= v0.65

Usage
-----

>>> import SessionState
>>>
>>> session_state = SessionState.get(user_name='', favorite_color='black')
>>> session_state.user_name
''
>>> session_state.user_name = 'Mary'
>>> session_state.favorite_color
'black'

Since you set user_name above, next time your script runs this will be the
result:
>>> session_state = get(user_name='', favorite_color='black')
>>> session_state.user_name
'Mary'

"""

import streamlit.report_thread as ReportThread
from streamlit.server.server import Server


class SessionState():
    """SessionState: Add per-session state to Streamlit."""
    def __init__(self, **kwargs):
        """A new SessionState object.

        Parameters
        ----------
        **kwargs : any
            Default values for the session state.

        Example
        -------
        >>> session_state = SessionState(user_name='', favorite_color='black')
        >>> session_state.user_name = 'Mary'
        ''
        >>> session_state.favorite_color
        'black'

        """
        for key, val in kwargs.items():
            setattr(self, key, val)


def get(**kwargs):
    """Gets a SessionState object for the current session.

    Creates a new object if necessary.

    Parameters
    ----------
    **kwargs : any
        Default values you want to add to the session state, if we're creating a
        new one.

    Example
    -------
    >>> session_state = get(user_name='', favorite_color='black')
    >>> session_state.user_name
    ''
    >>> session_state.user_name = 'Mary'
    >>> session_state.favorite_color
    'black'

    Since you set user_name above, next time your script runs this will be the
    result:
    >>> session_state = get(user_name='', favorite_color='black')
    >>> session_state.user_name
    'Mary'

    """
    # Hack to get the session object from Streamlit.

    session_id = ReportThread.get_report_ctx().session_id
    session_info = Server.get_current()._get_session_info(session_id)

    if session_info is None:
        raise RuntimeError('Could not get Streamlit session object.')

    this_session = session_info.session

    # Got the session object! Now let's attach some state into it.

    if not hasattr(this_session, '_custom_session_state'):
        this_session._custom_session_state = SessionState(**kwargs)

    return this_session._custom_session_state

Thanks. Works as expected.

New version of streamlit changed the internal usage of ReportThread

I was working until i've updated to streamlit==1.4.0

Works with 1.3.0

streamlit/streamlit#4099 (comment)