Update app.py

app.py

@@ -1,11 +1,48 @@
 import streamlit as st
 
-import streamlit as st
 import pandas as pd
 import numpy as np
 import altair as alt
 import pydeck as pdk
 
+@st.experimental_singleton
+ def get_database_session(_sessionmaker, url):
+     # Create a database connection object that points to the URL.
+     return connection
+
+s1 = get_database_session(create_sessionmaker(), st.session_state.qp))
+# Actually executes the function, since this is the first time it was
+# encountered.
+
+s2 = get_database_session(create_sessionmaker(), st.session_state.qp))
+# Does not execute the function. Instead, returns its previously computed
+# value - even though the _sessionmaker parameter was different
+# in both calls.
+
+
+
+# callback to update query param on selectbox change
+def update_params():
+    st.experimental_set_query_params(option=st.session_state.qp)
+    get_database_session(st.session_state.qp)
+
+options = st.selectbox(
+    "Param", ["cat", "dog", "mouse", "bat", "duck"], key="qp", on_change=update_params
+)
+
+query_params = st.experimental_get_query_params()
+
+# set the initial query param on first run
+# based on the default option in selectbox
+if not query_params:
+    st.experimental_set_query_params(option=st.session_state.qp)
+
+# display for debugging purposes
+query_params = st.experimental_get_query_params()
+st.write(query_params)
+
+
+
 # SETTING PAGE CONFIG TO WIDE MODE AND ADDING A TITLE AND FAVICON
 st.set_page_config(layout="wide", page_title="NYC Ridesharing Demo", page_icon=":taxi:")