associate DataFrameHolder to file

stand.py

@@ -47,9 +47,7 @@ if not new_df.equals(df) and not changed:
     restapi.data = df = new_df
 
 
-if not df.empty:
-    print("<<< write hdf")
-    df.to_hdf("output.h5", key="data")
+restapi.dfh.dump()
 
 
 print(">>> end of streamlit run")

tableapi.py

@@ -8,7 +8,7 @@ from utils.st_utils import rerun
 class TableAPI:
 
     def __init__(self):
-        self.dfh = DateFrameHolder()
+        self.dfh = DateFrameHolder("output.h5")
         self.sid = None
         self.changed = True
 

utils/df_utils.py

@@ -3,9 +3,13 @@ import pandas as pd
 
 class DateFrameHolder:
 
-    def __init__(self, df=None):
-        self.df = df or pd.DataFrame()
-#        self.df = pd.DataFrame.from_records([dict(a=1, b=2, c=3)] * 4) #TODO: remove
+    def __init__(self, fn):
+        self.fn = fn
+        self.df = try_load_df(fn)
+
+    def dump(self):
+        dump_non_empty_df(self.df, self.fn)
+
 
     def append(self, data):
         data = pd.DataFrame.from_records([data])
@@ -15,6 +19,31 @@ class DateFrameHolder:
         self.df = pd.DataFrame()
 
 
+    def __repr__(self):
+        head = self.fn + ":"
+        line = "-" * len(head)
+        df = str(self.df)
+        return "\n".join((head, line, df))
+
+
+
+def try_load_df(fn):
+    try:
+        df = pd.read_hdf(fn)
+        print(f">>> loaded dataframe from {fn}")
+    except FileNotFoundError:
+        df = pd.DataFrame()
+        print(">>> created empty dataframe")
+    return df
+
+def dump_non_empty_df(df, fn, key="data"):
+    if df.empty:
+        print("<<< skip dumping empty dataframe")
+        return
+    print(f"<<< dump dataframe to {fn}")
+    df.to_hdf(fn, key)
+
+
 
 from io import BytesIO