[Python] How to make streamlit session_state updated when I select a point on plotly_chart

I have this use case where I have a plotlychart :

import streamlit as st
import plotly.express as px

if "var" not in st.session_state:
st.session_state["var"] = 0

col3,col4 = st.columns(2)


def plot():
df = px.data.iris()
fig = px.scatter(
df,
x="sepal_width",
y="sepal_length",
color="species",
size="petal_length",
hover_data=["petal_width"],
)

event = st.plotly_chart(fig, key="iris", on_select="rerun")
event.selection
if len(event.selection.points)!=0:
st.session_state["var"] = event.selection.points[0]["x"]
# st.rerun()


with col3:
st.write(st.session_state["var"])

with col4:
plot()


my issue is when I select a point on the graph, logically the st.session_state["var"] should be updated directly …but it is not the case here…I have tried to use st.rerun() but it is enter in infinity loop…do you have any idea please to make st.session_state["var"] updated directly when I select a point ? I want to keep the order of cols as it is. thanks

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