move update code for postcode and word count to Python

Adds also tests for the new function to execute a SQL script.

test/python/test_db_utils.py

@@ -0,0 +1,33 @@
+"""
+Tests for DB utility functions in db.utils
+"""
+import psycopg2
+import pytest
+
+import nominatim.db.utils as db_utils
+
+def test_execute_file_success(temp_db, tmp_path):
+    tmpfile = tmp_path / 'test.sql'
+    tmpfile.write_text('CREATE TABLE test (id INT);\nINSERT INTO test VALUES(56);')
+
+    with psycopg2.connect('dbname=' + temp_db) as conn:
+        db_utils.execute_file(conn, tmpfile)
+
+        with conn.cursor() as cur:
+            cur.execute('SELECT * FROM test')
+
+            assert cur.rowcount == 1
+            assert cur.fetchone()[0] == 56
+
+def test_execute_file_bad_file(temp_db, tmp_path):
+    with psycopg2.connect('dbname=' + temp_db) as conn:
+        with pytest.raises(FileNotFoundError):
+            db_utils.execute_file(conn, tmp_path / 'test2.sql')
+
+def test_execute_file_bad_sql(temp_db, tmp_path):
+    tmpfile = tmp_path / 'test.sql'
+    tmpfile.write_text('CREATE STABLE test (id INT)')
+
+    with psycopg2.connect('dbname=' + temp_db) as conn:
+        with pytest.raises(psycopg2.ProgrammingError):
+            db_utils.execute_file(conn, tmpfile)