download_button always returns False when the data provided changes in each rerun

[mateusccoelho]

Checklist

• I have searched the existing issues for similar issues.
• I added a very descriptive title to this issue.
• I have provided sufficient information below to help reproduce this issue.

Summary

st.download_button's documentation says that it returns True if the button was clicked on the last run of the app. But I noticed that it always returns False when the data passed in the parameter data changes in the next rerun.

The browser download popup shows up normally, but the return doesn't work as intended.

Below I provide two examples.

1. Dummy example just to show it doesn't work. I generate random strings and pass them to st.download_button.
2. Problematic example because apparently nothing changes. The bytes are the same every rerun. But since a different object is generated inside the function each rerun, Streamlit doesn't recognize the click. I faced this problem and it was hard to debug.

Reproducible Code Example

#### Example 1 ####

import streamlit as st
from random import random

random_str = str(random())
print(random_str)

clicked = st.download_button(
    label='Download some text', 
    data=random_str
)
st.write(clicked)
print(clicked)

#### Example 2 ####

from io import BytesIO
import streamlit as st

def get_file_obj():
    random_bytes = bytes("idfisudfiusdhf".encode('utf-8'))
    file_obj = BytesIO(random_bytes)
    return file_obj

clicked = st.download_button(
    label='Download some text', 
    data=get_file_obj()
)
st.write(clicked)
print(clicked)

Steps To Reproduce

1. Use streamlit==1.26
2. Run examples 1 and 2 separately.

Expected Behavior

st.download_button return True when clicked, even if the data changes in the next rerun.

Current Behavior

Example 1 terminal output:

(env) [mateus@fedora download_test]$ streamlit run test.py 

  You can now view your Streamlit app in your browser.

  Local URL: http://localhost:8501
  Network URL: http://192.168.0.92:8501

0.39680310200698155
False
0.7461555731892388
False
0.5057767898133984
False
0.3176395196698075
False
0.5292348871076471
False

Example 2 terminal output:

(env) [mateus@fedora download_test]$ streamlit run test2.py 

  You can now view your Streamlit app in your browser.

  Local URL: http://localhost:8501
  Network URL: http://192.168.0.92:8501

False
False
False
False
False

Is this a regression?

• Yes, this used to work in a previous version.

Debug info

• Streamlit version: 1.26.0
• Python version: 3.10.11
• Operating System: Fedora 36
• Browser: Firefox 112.0.1

Additional Information

No response

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[kajarenc]

Hello @mateusccoelho and thank you for opening this issue.
I was able to reproduce the issue here and can confirm that this is a bug.

Looks like this is a regression in 1.26

We are working on fixing this issue

[mateusccoelho]

Hi @kajarenc, thanks for taking a look at it. For those who want to stick with 1.26 while the fix is in progress, I was able to solve the problem using @st.cache_resource and the parameter on_click.