Confusing behavior when state reloads an enum

Using Streamlit
,
1

I’m running Streamlit locally:
Python 3.12.3
streamlit 1.34.0

I am trying to store an enum in the Streamlit session state. When the page reloads (like after a button click) the enum appears to be set correctly, but it fails when I try to actually compare it against the enum.

I expected to be able to match the enum after the state reloaded after a button press. It fails.

I’m wondering if maybe the enum is getting redefined and it somehow just fails to see them as equal even when they are? Is this just a bad pattern for using in a SL app?

from enum import Enum, auto 
import streamlit as st

class State(Enum):
    RED = auto()
    GREEN = auto()
    BLUE = auto() 

st.title("State App")


default_values = {'current_index': 0, 'current_question': 0, 'score': 0, 
                  'selected_option': None, 'answer_submitted': False, 'state': State.RED}

for key, value in default_values.items():
    st.session_state.setdefault(key, value)


def toggle():
    print(f"In toggle, state variable is {st.session_state.state} {type(st.session_state.state)}")
    match st.session_state.state:
        case State.GREEN:
            print(f"In toggle function, matched to green")
            st.session_state.state = State.BLUE
        case State.RED:
            print(f"In toggle function, matched to red")    
            st.session_state.state = State.GREEN
        case State.BLUE:
            print(f"In toggle function, matched to blue")    
            st.session_state.state = State.RED        
        case _:
            print(f"In toggle function, no match. It's {st.session_state.state} {type(st.session_state.state)}")
            print(f"Equality: {State.GREEN==st.session_state.state}")
              
st.write(f"Current Color is {st.session_state.state} {type(st.session_state.state)}")
st.button('Next', on_click=toggle)   


match st.session_state.state:
    case State.GREEN:
        print(f"In body, state matched to green")
    case State.RED:
        print(f"In body, state matched to red")    
    case State.BLUE:
        print(f"In body, state matched to blue")            
    case _:
        print(f"In body, no match. It's {st.session_state.state}")

Output:

            
In body, state matched to red
In toggle, state variable is State.RED <enum 'State'>
In toggle function, matched to red
In if statement, it's green
In body, no match. It's State.GREEN
In toggle, state variable is State.GREEN <enum 'State'>
In toggle function, no match. It's State.GREEN <enum 'State'>
Equality: False
In body, no match. It's State.GREEN
2

This is expected behavior for Streamlit. When the page reruns, you define a new class. The object saved in Session State is an instance from the class defined during a previous rerun.

If you define your classes in external files and import them, you can get around this.

3

Thank you.

Another workaround I guess: I switched my Enum to an IntEnum and was able to use the match appropriately in this way.

4

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