Pr. now, we call sqlite3_column_count() for every iteration in the _pysqlite_query_execute() loop. If detect_types is set, we call it twice for every loop.

Suggesting to move it out of the loop and into the pysqlite_Statement object. In pysqlite_statement_create(), after sqlite3_prepare_v2(), if self->is_dml == 0 we fetch the column count: self->column_count = sqlite3_column_count(). Else, it's 0.


# SQLite API interaction examples (pseudo-code), as diffs
--- now
+++ patched

## Create table
 sqlite3_prepare_v2
+sqlite3_column_count
 sqlite3_bind_blob_parameter_count
 sqlite3_step
-sqlite3_column_count
 sqlite3_last_insert_rowid
 sqlite3_reset

## Triple insert (executemany)
 sqlite3_prepare_v2
 sqlite3_get_autocommit
 sqlite3_bind_blob_parameter_count
 sqlite3_bind_int64
 sqlite3_step
-sqlite3_column_count
 sqlite3_changes
 sqlite3_reset
 sqlite3_bind_blob_parameter_count
 sqlite3_bind_int64
 sqlite3_step
-sqlite3_column_count
 sqlite3_changes
 sqlite3_reset
 sqlite3_bind_blob_parameter_count
 sqlite3_bind_int64
 sqlite3_step
-sqlite3_column_count
 sqlite3_changes
 sqlite3_reset

This change breaks existing behaviour (see test below). Also, sqlite3_column_count() is implemented as a simple lookup in SQLite; it is never an expensive function. Suggests to add the following test instead:


diff --git a/Lib/sqlite3/test/dbapi.py b/Lib/sqlite3/test/dbapi.py
index 77fafe0930..d7a3b249ab 100644
--- a/Lib/sqlite3/test/dbapi.py
+++ b/Lib/sqlite3/test/dbapi.py
@@ -555,6 +555,17 @@ def test_last_row_id_insert_o_r(self):
         ]
         self.assertEqual(results, expected)
 
+    def test_column_count(self):
+        # Check that column count is updated correctly for cached statements
+        select = "select * from test"
+        res = self.cu.execute(select)
+        old_count = len(res.description)
+        # Add a new column and execute the cached select query again
+        self.cu.execute("alter table test add newcol")
+        res = self.cu.execute(select)
+        new_count = len(res.description)
+        self.assertEqual(old_count - new_count, 1)
+
 
 class ThreadTests(unittest.TestCase):
     def setUp(self):

New changeset 8363ac8607eca7398e568e1336154e1262a995a0 by Erlend Egeberg Aasland in branch 'main':
bpo-44041: Add test for sqlite3 column count (GH-25907)
https://github.com/python/cpython/commit/8363ac8607eca7398e568e1336154e1262a995a0