`sqlite3.Connection.execute()` exposes unrepresentable Argument Clinic default

[lpyu001]

Bug report

Bug description:

Summary

sqlite3.Connection.execute() currently exposes this text signature:

execute($self, sql, parameters=<unrepresentable>, /)

As a result, inspect.signature(sqlite3.Connection.execute) raises
ValueError. The correct Python default is (), while the C wrapper must
continue using NULL when the argument is omitted.

Evidence

The current Clinic definition in Modules/_sqlite/connection.c is:

parameters: object = NULL

When the argument is omitted, _pysqlite_query_execute() explicitly converts
the C NULL sentinel to an empty tuple:

if (second_argument == NULL) {
    second_argument = PyTuple_New(0);
}

Therefore these calls are equivalent:

con.execute("select 42")
con.execute("select 42", ())

The public documentation already specifies:

execute(sql, parameters=(), /)

sqlite3.Cursor.execute() also uses the correct Clinic pattern:

parameters: object(c_default="NULL") = ()

Reproduction

import inspect
import sqlite3

inspect.signature(sqlite3.Connection.execute)
# ValueError: builtin has invalid signature

CPython versions tested on:

CPython main branch

Operating systems tested on:

Linux

Linked PRs

• gh-155952: Fix unrepresentable Argument Clinic default for sqlite3.Connection.execute()  #155953
• gh-155952: Fix <unrepresentable> Argument Clinic defaults in several signatures #155954

[StanFromIreland]

I'd like to fix all of these at once, there seem to be quite a few more instances, e.g. datetime.datetime.combine or memoryview.hex.

[StanFromIreland]

Oh right, some are really unpresentable, and it'd be better to implement something like what was suggested in https://discuss.python.org/t/ac-null-defaults-prevent-correct-signatures-lets-add-inspect-unrepresentable-to-fix-this/30753. However others are indeed representable, and can be done in a sweep.

[lpyu001]

thanks,other than the two PRs I submitted, I haven't found any other issues like this ：)