add new SQL custom function, SPLIT

bookeeper/__main__.py

@@ -26,7 +26,7 @@ try:
   try:  # initializing DB
     dbconn = sqlite3.connect(params.dbpath)
     dbcur  = dbconn.cursor()
-    db.try_init(dbcur)
+    db.try_init(dbconn, dbcur)
   except Exception as e:
     raise Exception("failure while initializing DB", e)
 

bookeeper/db.py

@@ -1,6 +1,15 @@
 import sqlite3
 
-def try_init(cur):
+def _split(v, num):
+  if v is None:
+    return None
+  terms = v.split("/")
+  if num >= len(terms):
+    return None
+  return terms[num]
+
+def try_init(conn, cur):
+  conn.create_function("split", 2, _split)
   cur.execute("""
     CREATE TABLE IF NOT EXISTS entry (
       id   INTEGER    PRIMARY KEY AUTOINCREMENT,