session_state.md

Session State

Session state was added to Streamlit as an after thought to enable sharing variables between re-runs and across apps inside a multipage app.

Panels execution model is very different and session state can be handled automatically by storing variables in the applications namespace.

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Migration Steps

• Move your session state to the applications namespace, i.e. to variables defined in your application file.

Example

Dynamic Layout Example

Streamlit Dynamic Layout Example

import random
from uuid import uuid4

import streamlit as st

st.session_state.setdefault("rows", {})

def create_row(hex_id=None):
    if hex_id is None:
        hex_id = uuid4().hex
        value = random.randint(0, 100)
        st.session_state.rows[hex_id] = value
    else:
        value = st.session_state.rows[hex_id]

    st.number_input("Enter a number", value=value, key=f"num_{hex_id}")

st.title("Dynamically add new rows")

button_cols = st.columns(2)
with button_cols[0]:
    add_row = st.button("Add new row", use_container_width=True)
with button_cols[1]:
    clear_rows = st.button("Clear all rows", use_container_width=True)

if clear_rows:
    st.session_state.rows = {}

for hex_id in st.session_state.rows.keys():
    create_row(hex_id=hex_id)

if add_row:
    create_row()

With Streamlit you need session state to keep track of the dynamically created rows.

Panel Dynamic Layout Example

import random

import panel as pn

pn.extension(sizing_mode="stretch_width", template='bootstrap')

def create_row(event):
    value = random.randint(0, 100)
    row = pn.widgets.TextInput(name="Enter a number", value=str(value))
    rows.append(row)

rows = pn.Column()
add_row = pn.widgets.Button(name="Add new row", on_click=create_row)
clear_rows = pn.widgets.Button(name="Clear all rows", on_click=lambda event: rows.clear())

pn.Column(
    "# Dynamically add new rows",
    pn.Row(add_row, clear_rows),
    rows
).servable()

As the Panel script is only executed once per session the rows objects will keep track of your session state.