Bug report

Bug description:

In Python 3.11, the code object of a lambda function that returns a constant value used to have location information provided for the LOAD_CONST bytecode:

import dis
f = lambda: ...
for pos in f.__code__.co_positions():
    print(*pos)
dis.dis(f)

This outputs, in Python 3.11:

2 2 0 0
2 2 12 15
2 2 0 0
  2           0 RESUME                   0
              2 LOAD_CONST               1 (Ellipsis)
              4 RETURN_VALUE

However, since Python 3.12, where RETURN_CONST was introduced, the same code now outputs:

2 2 0 0
2 2 0 0
  2           RESUME                   0
              RETURN_CONST             1 (Ellipsis)

with no precise location information found in any of the bytecode produced.

Note that a regular function that returns a constant value correctly provides precise location information for RETURN_CONST in Python 3.12+:

import dis
def f():
    return ...
for pos in f.__code__.co_positions():
    print(*pos)
dis.dis(f)

which outputs:

2 2 0 0
3 3 11 14
  2           RESUME                   0

  3           RETURN_CONST             1 (Ellipsis)

CPython versions tested on:

3.11, 3.12, CPython main branch

Operating systems tested on:

Linux, Windows

Linked PRs

• gh-120722: Propogate instruction location in optimization of LOAD_CONST + RETURN_VALUE with RETURN_CONST #120723
• gh-120722: Set position on RETURN_VALUE in lambda #120724
• [3.13] gh-120722: Set position on RETURN_VALUE in lambda (GH-120724) #120738
• [3.12] gh-120722: Set position on RETURN_VALUE in lambda (GH-120724) #120739