IndexError when accessing dis.cmp_op[instruction.arg] in Python 3.13 but not in 3.10

[mouchen626]

Bug report

Bug description:

The following code, which works without error in Python 3.10, raises an IndexError in Python 3.13 when trying to access dis.cmp_op[instruction.arg]:

import dis

def my_fun(a, b):
    return a <= b

for instruction in dis.get_instructions(my_fun):
    if instruction.opname == 'COMPARE_OP':
        print(dis.cmp_op[instruction.arg])

CPython versions tested on:

3.13

Operating systems tested on:

No response

[brianschubert]

This is expected. The meaning of the opcode argument changed in 3.13. Quoting the docs for COMPARE_OP:

COMPARE_OP(opname)

Performs a Boolean operation. The operation name can be found in cmp_op[opname >> 5]. If the fifth-lowest bit of opname is set (opname & 16), the result should be coerced to bool.

Changed in version 3.13: The fifth-lowest bit of the oparg now indicates a forced conversion to bool.

You’ll need to use dis.cmp_op[instruction.arg >> 5] instead in 3.13.

Note that there was also a similar change in 3.12

Changed in version 3.12: The cmp_op index is now stored in the four-highest bits of oparg instead of the four-lowest bits of oparg.

Side note: I’m not sure why the “Changed in 3.12” banner is missing in the 3.13+ docs. It seems like that’s something that should be kept around / clarified.