[DB-SIG] Improved support for prepared SQL statements

[SF Markus Elfring]

Hello,

An interface for parameterised SQL statements (working with
placeholders) is provided by the execute() method from the Cursor class
at the moment.
https://docs.python.org/3/library/sqlite3.html#sqlite3.Cursor.execute

I assume that the "SQL Statement Object" from the SQLite C interface is
reused there already.
http://sqlite.org/c3ref/stmt.html

I imagine that it will be more efficient occasionally to offer also a
base class like "prepared_statement" so that the parameter specification
does not need to be parsed for every passed command.
I suggest to improve corresponding preparation and compilation
possibilities.
https://bugs.python.org/issue22956

Regards,
Markus