Python: Number of rows affected by cursor.execute("SELECT ...)

From PEP 249, which is usually implemented by Python database APIs:

Cursor Objects should respond to the following methods and attributes:

[…]

.rowcount
This read-only attribute specifies the number of rows that the last .execute*() produced (for DQL statements like 'select') or affected (for DML statements like 'update' or 'insert').

But be careful—it goes on to say:

The attribute is -1 in case no .execute*() has been performed on the cursor or the rowcount of the last operation is cannot be determined by the interface. [7]

Note:
Future versions of the DB API specification could redefine the latter case to have the object return None instead of -1.

So if you've executed your statement, and it works, and you're certain your code will always be run against the same version of the same DBMS, this is a reasonable solution.