Rerun when file system/database/some other external data source changes

This is an issue to cover the topics not addressed within PR https://github.com/streamlit/streamlit/pull/2060 that were raised within the issue https://github.com/streamlit/streamlit/issues/653.

Below are copied in some key comments

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The key goals personally for an API that is able to rerun when an external data source changes are listed below:

• Selected module imports
  • To support live-reloading while building streamlit apps within the pymedphys library (https://github.com/pymedphys/pymedphys/tree/master/pymedphys/_gui/streamlit).
  • Allows for a significantly faster development iteration loop within the framework of a Python library/package.
• Directory updates
  • To support deploying a plugin based GUI where pymedphys users can add their own streamlit apps and submit them upstream. The index/landing page of the GUI would live update when new apps are added to the index
  • Some key ideas are the following – https://github.com/streamlit/streamlit/issues/543#issuecomment-660410027
• File updates
  • To make it so that images collected from our linear accelerator (https://www.elekta.com/radiotherapy/) at work can be live streamed to the application with analysis undergone in real time
• Database triggered updates
  • To have changes within our radiation oncology information system (https://www.elekta.com/software-solutions/care-management/mosaiq-radiation-oncology/) automatically trigger app reruns.

_Originally posted by @SimonBiggs in https://github.com/streamlit/streamlit/pull/2060#issuecomment-704016152_

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Is there a way to get the current session from within a watchdog thread? For example, see the following use case:

After you create a thread (but before you start it), you can call report_thread.add_report_ctx(...) to attach a ReportContext object (which contains the session_id) to that thread.

Of course, this requires that thread creation be under your control - which (I think?) does not apply for watchdog.

What I’d suggest in this situation - with the caveat that it’s been a while since I looked at this code - is to create a separate thread (with the ReportContext attached) that simply handles watchdog file-changed events that are raised from within the watchdog thread. (You’ll need to set up some method of communicating between the two threads, like a thread safe queue or something.)

Does that make sense, and is it possible for your use case?

_Originally posted by @tconkling in https://github.com/streamlit/streamlit/pull/2060#issuecomment-703945085_

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Some ideas for various possible APIs:

• st.experimental_autoreload(modules)
  • modules can be an iterable of imported modules (types.ModuleType) or a single imported module.
  • Flags it so that any changes in these modules will cause the streamlit app to auto-reload.
  • See https://github.com/pymedphys/pymedphys/blob/1995dd1177d6f6b57dbf81dc251092d2ab4e5d9b/pymedphys/_gui/streamlit/dashboard.py#L27 for usage.
• st.experimental_file_contents(path)
  • Returns the contents of a file and triggers a rerun whenever the contents of that file changes (reusing the same logic as used for autoreload).

– https://github.com/streamlit/streamlit/issues/653#issuecomment-679853730

and

• st.experimental_directory_tree('path/to/directory', recursive=False)
  • Returns a list of file paths within a given directory, triggers a rerun whenever that directory tree itself changes (file name changed or file added or deleted).
  • This would support something like the default index.py I described over at https://github.com/streamlit/streamlit/issues/543#issuecomment-660410027

– https://github.com/streamlit/streamlit/issues/653#issuecomment-680423424

_Originally posted by @SimonBiggs in https://github.com/streamlit/streamlit/pull/2060#issuecomment-703901760_

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[firla]

Anyone? Thx

[firla]

Hi. I am currently researching web app frameworks for a new project, so I am new to the topic. Streamlit sounds wonderful and is currently my favorite. However, I absolutely need the “rerun when database (redis keys) changes” feature. I have read #2060 and #2180, but I am not yet sure if the feature is available (per st.experimental_rerun).

Thank you for a brief info or links to related documentation.