🎬 : Improved file uploader and camera input to call its on_change handler only when necessary

[kajarenc]

We need that change to prevent on_change call for file_uploader on rerun.

📚 Context

Fix for #4256 .
When file uploaded to file_uploader, each rerun triggers on_change callback call.
This happens because we in session_state.py we check is old and new values are the same.
But since st.file_uploader returns a new UploadedFile object each time in deserialize method values are not equal.

I override __eq__ method for UploadedFile to check equality via underlying UploadedFileRecs ids

• What kind of change does this PR introduce?

  • Bugfix
  • Feature
  • Refactoring
  • Other, please describe:

🧠 Description of Changes

• Add bullet points summarizing your changes here

  • This is a breaking API change
  • This is a visible (user-facing) change

Revised:

Insert screenshot of your updated UI/code here

Current:

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🧪 Testing Done

• Screenshots included
• Added/Updated unit tests
• Added/Updated e2e tests

🌐 References

Does this depend on other work, documents, or tickets?

• Issue: Closes #XXXX

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[vdonato]

This LGTM, but I think we'll also want to check in with core platform to verify that doing this won't have any unintended consequences

[tconkling]

This seems fine to me and I don't think it interferes with anything we're doing over here -

BUT, it'd be ideal if it had a test to prevent against regressions of the bug it's addressing. (Just something that asserts that the fileuploader callback isn't called when the file hasn't changed.)

[tconkling]

To be really correct, __eq__ should typecheck its argument (and we might as well also type-annotate the function)

def __eq__(self, other: object) -> bool:
  if not isinstance(other, UploadedFile):
    return NotImplemented
  return self.id == other.id

(This StackOverflow has more details about the weird "return NotImplemented" line: https://stackoverflow.com/questions/878943/why-return-notimplemented-instead-of-raising-notimplementederror)

[Ericarru]

Hi, maybe it's not the place but i am using streamlit 1.27 and I have checked for 1.28 and 1.29 too that "on change" function is executing every time the app is reloaded. Here snippet of my app:

import streamlit as st


def session_state_counter():
    if "counter" in st.session_state:
        st.session_state.counter = st.session_state.counter + 1
    else:
        st.session_state.counter = 1


file_raw = st.file_uploader(
    "Upload_file",
    on_change=session_state_counter(),  # on change does not work
)

st.button("Click me to test counter :)")

st.write(f"Counter: {st.session_state.counter}")