Streamlit Paginated Example

pages.py

import numpy as np
import streamlit as st

from .streamlit_utils import SessionState

session_state = SessionState.get(page=1)


def main():
    # Render the readme as markdown using st.markdown.
    readme_text = st.markdown('''
    # Instructions

    Lorem ipsum dolor sit amet, consectetur adipiscing elit. Sed vel lorem tincidunt, 
    congue orci id, pretium augue. Curabitur facilisis malesuada justo. Sed tincidunt 
    metus sed arcu blandit efficitur. Vestibulum ut neque sed diam dapibus imperdiet 
    id sit amet ante. In in sollicitudin est, ut bibendum lectus. Curabitur posuere 
    cursus dui. Nullam interdum eu nunc ac bibendum. Etiam id dolor laoreet nulla euismod 
    tristique. Nulla mollis condimentum auctor. Mauris ut diam ante. Maecenas at mauris 
    vulputate, hendrerit erat in, viverra libero. Nulla viverra lacus vitae urna hendrerit 
    fringilla. Aliquam pharetra justo vitae neque semper, a consequat lorem varius.
    ''')

    # Add a selector for the app mode on the sidebar.
    st.sidebar.title("What to do")
    app_mode = st.sidebar.selectbox(
        "Choose the app mode",
        ["Instructions", "Show paginated content"]
    )
    if app_mode == "Instructions":
        st.sidebar.success('To continue select an option in the dropdown menu.')
    elif app_mode == "Show paginated content":
        readme_text.empty()
        prev_page = st.button('prev')
        if prev_page:
            session_state.page -= 1
        next_page = st.button('next')
        if next_page:
            session_state.page += 1
        st.write(f'page: {session_state.page}')
        load_data(page=session_state.page)


def load_data(page=1):
    data = np.arange(1, 100)
    page = max(page, 1)
    per_page = 10
    start = (page - 1) * per_page
    end = page * per_page
    results = data[start:end]

    for i in results:
        st.subheader(i)
        st.text('Lorem ipsum dolor sit amet, consectetur adipiscing elit.')


if __name__ == "__main__":
    main()

streamlit_utils.py

'''
An example implementation from https://discuss.streamlit.io/t/preserving-state-across-sidebar-pages/107
'''

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()

        session = None
        session_infos = Server.get_current()._session_infos.values()

        for session_info in session_infos:
            if session_info.session._main_dg == ctx.main_dg:
                session = session_info.session

        if 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 getattr(session, '_custom_session_state', None):
            session._custom_session_state = SessionState(**kwargs)

        return session._custom_session_state

I'm getting this error when I import SessionState:

AttributeError: 'ReportSession' object has no attribute '_main_dg'
Traceback:
File "e:\anaconda3\envs\myenv\lib\site-packages\streamlit\ScriptRunner.py", line 314, in _run_script
exec(code, module.dict)
File "CompareModels_img.py", line 139, in
session_state = SessionState.get(question=1)
File "streamlit_utils.py", line 61, in get
if session_info.session._main_dg == ctx.main_dg:

any idea how to fix this?

https://discuss.streamlit.io/t/new-streamlit-release-0-54-0/1776

see this announcement