Streamlit deletes sys.modules on reload

[MattSegal]

Summary

When you run streamlit and use the reload feature it will delete entries from the sys.modules dict, causing a KeyError.

Steps to reproduce

I can't seem to build a small reproducible example.
It's happening to me on https://github.com/monash-emu/AuTuMN for commit 1eab4e862ae9e9aa99d489e98f13a78383cb5834

The steps to reproduce are:

• run streamlit
• make file change in watched module
• reload page with r
• see error

video of reproduction: https://www.loom.com/share/74f242f7f2154708a8f54f6dff879101

Expected behavior:

No items are deleted from sys.modules on reload

Actual behavior:

Items are deleted from sys.modules on reload

Is this a regression?

Dunno

Debug info

• Streamlit version: 0.58.0
• Python version: 3.6.8
• Using virtualenv
• OS version: Ubuntu 18.04.4 LTS
• Browser version: Chromium ???

Additional information

Prior discussion: https://discuss.streamlit.io/t/keyerror-warnings/2474/6

I believe this line of code is the cause:

streamlit/lib/streamlit/watcher/LocalSourcesWatcher.py

Line 114 in 018f49f

del sys.modules[wm.module_name]

I was able to stop the error from happening by hacking in a fix to that module (see linked discussion)

[batmanscode]

I have the same (probably) issue. I get a KeyError as well whenever it reloads. I wish I saw the discussion before I reinstalled conda lol.

For me the problem line of code was results = model.predict(X_test) and this always worked fine on streamlit run but KeyError after a reload.

I'm using conda on windows, streamlit version: 0.62.1, python: 3.8.3

Fixed by adding:

import warnings
warnings.filterwarnings('ignore')

[jrieke]

Closing, since this seems to be covered in a reproducible way in #6404