Hot-reloading not working when a module is imported with `from foo import bar`

Summary

@Icerman observes hat hot reloading works as expected when modules are imported like:

import foo.bar

or

import foo.bar as bar

but when importing the same module using:

from foo import bar

then its changes are ignored.

Steps to reproduce

Steps to reproduce are described below.

Debug info

@MarcSkovMadsen gave his system information below.

Additional information

This is the first of two bugs based on this awesome-streamlit issue. The second bug is this.

[lcerman]

Hello I have run in the same issue recently. It seems that auto-reload works as expected when modules are imported like:

import foo.bar

or

import foo.bar as bar

but when I import the same module using:

from foo import bar

then its changes are ignored.

---

Steps to reproduce:

1. create new venv with only streamlit installed (version 0.47.4).
2. create following files:

main_ok.py:

import streamlit as st
import foo.bar

st.markdown('Main file')

foo.bar.fn()

main_ok2.py:

import streamlit as st
import foo.bar as bar

st.markdown('Main file')

bar.fn()

main_ko.py:

import streamlit as st
from foo import bar

st.markdown('Main file')

bar.fn()

foo/bar.py:

import streamlit as st

def fn():
    st.markdown('Function in submodule.')

1. changes in foo/bar.py are reflected when run as streamlit run main_ok.py or streamlit run main_ok.py2 but ignored when run the app as streamlit run main_ko.py

---

My system is Ubuntu 18.04 running inside WSL at Windows 10, Python 3.6.8.

[tconkling]

Notes, as I’m investigating:

• We properly register a filewatcher for from foo import bar modules
• The first time through LocalSourcesWatcher.update_watched_modules, sys.modules includes these modules as expected
• But upon rerun, sys.modules seems to… lose them?
• It turns out we’re doing sys.modules pruning from LocalSourcesWatcher.on_file_changed (removing any watched file that changes from sys.modules), but I’m not sure why. – Per @tvst, this is to force python to reload that module.
• If we remove this logic from on_file_changed, changing the module causes a re-run as expected. But: it’s as if the module itself is not being reloaded; no changes are reflected.
• Do we need to reload() watched modules before re-running?

https://stackoverflow.com/questions/7271082/how-to-reload-a-modules-function-in-python

• Based on the above, I think what needs to happen is: – When we detect a file change: – Recursively… reload that file and every file that depends on it?? – What we really want to do is just throw out everything and reload it all.
• We’re modifying sys.modules all over the place. Do we need to be more careful with this, across multiple threads? (Or maybe we don’t support hot-reloading if > 1 user is connected?)