Update app.py

app.py

@@ -1,25 +1,28 @@
-
 import streamlit as st
 
-def query_params():
-    st.write("""
-    # Introducing Query Params
-    We have added to our experimental namespace the ability to get and set
-    query parameters. With these query params, you can bookmark or share your app
-    in various states. Thanks [@zhaoooyue](https://github.com/zhaoooyue) for the
-    contribution!
-    """)
-    with st.echo("below"):
-        radio_list = ['Eat', 'Sleep', 'Both']
-        query_params = st.experimental_get_query_params()
+# query params exist
+try:
+    options = ['cat', 'dog', 'mouse', 'bat', 'duck']
+
+    query_params = st.experimental_get_query_params()
+    query_option = query_params['option'][0] #throws an exception when visiting http://host:port
+
+    option_selected = st.sidebar.selectbox('Pick option',
+                                            options,
+                                            index=options.index(query_option))
+    if option_selected:
+        st.experimental_set_query_params(option=option_selected)
+
+# run when query params don't exist. e.g on first launch
+except: # catch exception and set query param to predefined value
+    options = ['cat', 'dog', 'mouse', 'bat', 'duck']
+    st.experimental_set_query_params(option=options[1]) # defaults to dog
+
+    query_params = st.experimental_get_query_params()
+    query_option = query_params['option'][0]
 
-        # Query parameters are returned as a list to support multiselect.
-        # Get the first item in the list if the query parameter exists.
-        default = int(query_params["activity"][0]) if "activity" in query_params else 0
-        activity = st.radio(
-            "What are you doing at home during quarantine?",
-            radio_list,
-            index = default
-        )
-        if activity:
-            st.experimental_set_query_params(activity=radio_list.index(activity))
+    option_selected = st.sidebar.selectbox('Pick option',
+                                            options,
+                                            index=options.index(query_option))
+    if option_selected:
+        st.experimental_set_query_params(option=option_selected)