added in-memory conversion to excel file

utils/df_utils.py

@@ -16,3 +16,14 @@ class DateFrameHolder:
 
 
 
+from io import BytesIO
+
+
+def to_excel_binary(df):
+    with BytesIO() as out:
+        df.to_excel(out)
+        res = out.getvalue()
+    return res
+
+
+