bpo-44041: Only call sqlite3_column_count() if needed

Author: Erlend E. Aasland

Modules/_sqlite/cursor.c

@@ -147,7 +147,8 @@ pysqlite_build_row_cast_map(pysqlite_Cursor* self)
         return -1;
     }
 
-    for (i = 0; i < sqlite3_column_count(self->statement->st); i++) {
+    int column_count = self->statement->column_count;
+    for (i = 0; i < column_count; i++) {
         converter = NULL;
 
         if (self->connection->detect_types & PARSE_COLNAMES) {
@@ -547,9 +548,7 @@ _pysqlite_query_execute(pysqlite_Cursor* self, int multiple, PyObject* operation
         }
 
         assert(rc == SQLITE_ROW || rc == SQLITE_DONE);
-        Py_BEGIN_ALLOW_THREADS
-        numcols = sqlite3_column_count(self->statement->st);
-        Py_END_ALLOW_THREADS
+        numcols = self->statement->column_count;
         if (self->description == Py_None && numcols > 0) {
             Py_SETREF(self->description, PyTuple_New(numcols));
             if (!self->description) {

Modules/_sqlite/statement.c

@@ -58,6 +58,7 @@ int pysqlite_statement_create(pysqlite_Statement* self, pysqlite_Connection* con
 
     self->st = NULL;
     self->in_use = 0;
+    self->column_count = 0;
 
     assert(PyUnicode_Check(sql));
 
@@ -103,10 +104,20 @@ int pysqlite_statement_create(pysqlite_Statement* self, pysqlite_Connection* con
 
     self->db = connection->db;
 
-    if (rc == SQLITE_OK && pysqlite_check_remaining_sql(tail)) {
+    if (rc != SQLITE_OK) {
+        return rc;
+    }
+
+    if (pysqlite_check_remaining_sql(tail)) {
         (void)sqlite3_finalize(self->st);
         self->st = NULL;
-        rc = PYSQLITE_TOO_MUCH_SQL;
+        return PYSQLITE_TOO_MUCH_SQL;
+    }
+
+    if (!self->is_dml) {
+        Py_BEGIN_ALLOW_THREADS
+        self->column_count = sqlite3_column_count(self->st);
+        Py_END_ALLOW_THREADS
     }
 
     return rc;

Modules/_sqlite/statement.h

@@ -40,6 +40,7 @@ typedef struct
     PyObject* sql;
     int in_use;
     int is_dml;
+    int column_count;
     PyObject* in_weakreflist; /* List of weak references */
 } pysqlite_Statement;