made onchange a class

app.py

@@ -35,8 +35,13 @@ with st.spinner("Loading Model"):
     
 select_idx = None
 
-def onchange():
-    st.write("this has changed")
+class OnChange():
+    def __init__(self, idx):
+        self.idx = idx
+
+    def __call__(self):
+        st.write(f"the idx is: {self.idx}")
+        st.write(f"the sample_image is {sample_image}")
 
 st.sidebar.title("Select a sample image")
 
@@ -47,7 +52,7 @@ sample_image = st.sidebar.selectbox(
     "",
     sample_images,
     index = 0 if select_idx is None else select_idx,
-    on_change=onchange
+    on_change=OnChange(index)
 )
 
 st.sidebar.title("Select a Subreddit")