Revert "remove BEGIN and COMMIT"

This reverts commit 006657e.

Author: Kareem Zidane

src/cs50/sql.py

@@ -20,31 +20,24 @@ def __init__(self, url, **engine_kwargs):
         dialect = self._session.get_bind().dialect
         self._is_postgres = dialect.name in {"postgres", "postgresql"}
         self._sanitize_statement = statement_factory(dialect)
-        self._outside_transaction = True
+        self._autocommit = False
 
     def execute(self, sql, *args, **kwargs):
         """Execute a SQL statement."""
         statement = self._sanitize_statement(sql, *args, **kwargs)
-        try:
-            with raise_errors_for_warnings():
-                result = self._session.execute(statement)
-        except sqlalchemy.exc.IntegrityError as exc:
-            _logger.debug(termcolor.colored(str(statement), "yellow"))
-            if self._outside_transaction:
-                self._session.remove()
-            raise ValueError(exc.orig) from None
-        except (sqlalchemy.exc.OperationalError, sqlalchemy.exc.ProgrammingError) as exc:
-            self._session.remove()
-            _logger.debug(termcolor.colored(statement, "red"))
-            raise RuntimeError(exc.orig) from None
-
         if statement.is_transaction_start():
-            self._outside_transaction = False
+            self._autocommit = False
+
+        if self._autocommit:
+            self._session.execute("BEGIN")
 
-        _logger.debug(termcolor.colored(str(statement), "green"))
+        result = self._execute(statement)
+
+        if self._autocommit:
+            self._session.execute("COMMIT")
 
         if statement.is_transaction_end():
-            self._outside_transaction = True
+            self._autocommit = True
 
         if statement.is_select():
             ret = fetch_select_result(result)
@@ -55,11 +48,28 @@ def execute(self, sql, *args, **kwargs):
         else:
             ret = True
 
-        if self._outside_transaction:
+        if self._autocommit:
             self._session.remove()
 
         return ret
 
+    def _execute(self, statement):
+        with raise_errors_for_warnings():
+            try:
+                result = self._session.execute(statement)
+            except sqlalchemy.exc.IntegrityError as exc:
+                _logger.debug(termcolor.colored(str(statement), "yellow"))
+                if self._autocommit:
+                    self._session.remove()
+                raise ValueError(exc.orig) from None
+            except (sqlalchemy.exc.OperationalError, sqlalchemy.exc.ProgrammingError) as exc:
+                self._session.remove()
+                _logger.debug(termcolor.colored(statement, "red"))
+                raise RuntimeError(exc.orig) from None
+
+            _logger.debug(termcolor.colored(str(statement), "green"))
+            return result
+
     def _last_row_id_or_none(self, result):
         if self._is_postgres:
             return self._get_last_val()