Stuff written to st.empty() immediately gets overwritten

šŸŽˆ Using Streamlit
1

Summary

Iā€™m trying to use a st.empty() placeholder at the bottom of my page, which I write to via callback. Unfortunately, anything I write to the st.empty() is immediately overwritten next app cycle. I was hoping to ā€œreserveā€ a place at the bottom of the page, then write output there after doing some processing.

Steps to reproduce

Code snippet:

import streamlit as st

def process_user_input():
    user_input = st.session_state["user_input"]
    
    output = do_some_stuff_here()

    output_placeholder.text_area(label="Output", value=output)

st.text_area(label="User Input", placeholder="Enter stuff here", key="user_input", on_change=process_user_input)

output_placeholder = st.empty()

Expected behavior:

I thought this would let me write to the output_placeholder spot, replacing it with a st.text_area() once there was a user response.

Actual behavior:

The st.text_area() DOES show up for a split second, itā€™s just immediately overwritten.

2

Iā€™m surprised this doesnā€™t throw an error, actually. The callback executes before the script (namely before your empty container is defined). In any case, your script always ends with output_placeholder = st.empty() so that 's always the last thing to execute.

Try storing your output in Session State then simply displaying it at the end.

import streamlit as st

def process_user_input():
    user_input = st.session_state["user_input"]
    output = f"Output from input: {user_input}"
    st.session_state["output"] = output

st.text_area(label="User Input", placeholder="Enter stuff here", key="user_input", on_change=process_user_input)
if "output" in st.session_state:
    st.write(st.session_state["output"])

If you only want to display your result briefly and then have it go away. You can delete the key from session state after displaying it:

del st.session_state["output"]