Prevent page refresh in streamlit

Question

In my streamlit app, I use a form for the user to input some filters (date-range etc). On submit, a visualization is shown with a download-button below to download a CSV of the shown data

Something like (pseudo-code)

with st.form(key="input_parameters"):
    choices = st.multiselect(...) 
    .... more inputs here
    submitted = st.form_submit_button("Submit")

if submitted:
   data = get_data(choices,...)
   st.linechart(data)
   st.download_button("Download CSV",data)

my problem is that after the user clicked the download_button, the page reloads and the graphics disappears. How can I solve that? Is there a way to resubmit the form with the same input again?

Answer 1

The problem is that the script is rerun after the user presses the submit button, resetting submitted to False.

You can circumvent this behaviour by adding a flag to the session state and check if it was previously set. Maybe there are more elegant ways of doing this, but this is one way:

import streamlit as st
import pandas as pd
import numpy as np

dummy_data = pd.DataFrame(np.random.randint(0, 100, size=(100, 2)), columns=['X', 'Y'])
try:
    # check if the key exists in session state
    _ = st.session_state.keep_graphics
except AttributeError:
    # otherwise set it to false
    st.session_state.keep_graphics = False

with st.form(key="input_parameters"):
    choices = st.multiselect('Choose me', ['Plot1', 'Plot2'])
    submitted = st.form_submit_button("Submit")

if submitted or st.session_state.keep_graphics:
    st.line_chart(dummy_data)
    st.session_state.keep_graphics = True
    st.download_button("Download CSV", dummy_data.to_csv())