empty dataframe

app.py

@@ -160,7 +160,7 @@ if cobie_file_button:
     tabs = cobie_file.sheet_names
 
 selected_column = None
-df = pd.DataFrame
+df = pd.DataFrame()
 
 if tabs:
     selected_sheet = st.selectbox(
@@ -168,11 +168,13 @@ if tabs:
         tabs,
     )
 
-    df = cobie_file.parse(selected_sheet)
+    if selected_sheet:
+        
+        df = cobie_file.parse(selected_sheet)
 
     if type(df) == pd.DataFrame:
 
-        # st.write(df)
+        st.write(df)
         columns = df.columns
         selected_column = st.selectbox(
             'Select column with revit ids',