`st.write`/`st.json` render sets as strings

Summary

When I try to save a set in st.session_state and write it to the screen using st.write, the set is printed out as a string.

Steps to reproduce

Code snippet:

import streamlit as st

if ["list"] not in st.session_state:
    st.session_state["list"] = []
if ["dict"] not in st.session_state:
    st.session_state["dict"] = {}
if ["set"] not in st.session_state:
    st.session_state["set"] = set()

st.write(st.session_state)

Expected behavior:

{
  "list": [],
  "set": set(),
  "dict": {}
}

Actual behavior:

{
  "list": [],
  "set": "set()",
  "dict": {}
}

Is this a regression?

No.

Debug info

• Streamlit version: 1.10
• Python version: 3.8
• Using virtualenv
• OS version: Ubuntu 20.04 on WSL2
• Browser version: Firefox 102

[sfc-gh-kbregula]

Alternatively, we can create our own serialization instead of JSON, which allows two additional types to be transferred: set and tuple.

When it comes to displaying in UI, we can adopt a pretty-format format, that is, add a new label that describes the type.

Before:

{
  "list": [],
  "set": "set()",
  "dict": {}
}

After:

Object {
  "list": Array [],
  "set": Set {},
  "dict": Object {}
}

This, however, will require us to make a fork of the library - react-json-view, which will support our data serialization format.

[vdonato]

@sfc-gh-tszerszen +1 to this behavior. I think it’d probably be more desirable than nicely rendering it as a python set since, even though the types aren’t quite right, it’d be more useful for a user to be able to expand/collapse the list with existing functionality in st.json.

I think this is a small decision that the product team would have to make the final call on, so CCing @jrieke to take a look at when he’s back from vacation 🌴