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A possible design for doing per-session persistent state in Streamlit
"""Hack to add per-session state to Streamlit.
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.ReportThread as ReportThread
from streamlit.server.Server import Server
class SessionState(object):
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.
ctx = ReportThread.get_report_ctx()
this_session = None
current_server = Server.get_current()
if hasattr(current_server, '_session_infos'):
# Streamlit < 0.56
session_infos = Server.get_current()._session_infos.values()
else:
session_infos = Server.get_current()._session_info_by_id.values()
for session_info in session_infos:
s = session_info.session
if (
# Streamlit < 0.54.0
(hasattr(s, '_main_dg') and s._main_dg == ctx.main_dg)
or
# Streamlit >= 0.54.0
(not hasattr(s, '_main_dg') and s.enqueue == ctx.enqueue)
):
this_session = s
if this_session is None:
raise RuntimeError(
"Oh noes. Couldn't get your Streamlit Session object"
'Are you doing something fancy with threads?')
# 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
@treuille

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treuille commented Oct 24, 2019

I would add

__all__ = ['get'] 

to the end of this.

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