[Python-Dev] Intention to accept PEP 552 soon (deterministic pyc files)

[Guido van Rossum]

Honestly I think the API for accessing historic pyc headers should itself
also be 3rd party. CPython itself should not bother (backwards
compatibility with pyc files has never been a feature).

On Thu, Oct 5, 2017 at 6:44 AM, Barry Warsaw <barry at python.org> wrote:

> On Oct 4, 2017, at 13:53, Benjamin Peterson <benjamin at python.org> wrote:
>
> > It might be helpful to enumerate the usecases for such an API. Perhaps a
> > narrow, specialized API could satisfy most needs in a supportable way.
>
> Currently `python -m dis thing.py` compiles the source then disassembles
> it.  It would be kind of cool if you could pass a .pyc file to -m dis, in
> which case you’d need to unpack the header to get to the code object.  A
> naive implementation would unpack the magic number and refuse to
> disassemble any files that don’t match whatever that version of Python
> understands.  A more robust (possibly 3rd party) implementation could
> potentially disassemble a range of magic numbers and formats, and an API to
> get at the code object and metadata would help.
>
> I was thinking about the bytecode hacking that some debuggers do.  This
> API would help them support multiple versions of Python.  They could use
> the API to discover what pyc format was in use, extract the code object,
> hack the bytecode and possibly rewrite a new PEP 3147 style pyc file with
> the debugger bytecodes inserted.
>
> Third party bytecode optimizers could use the API to unpack multiple
> versions of pyc files, do their optimizations, and rewrite new files with
> the proper format.
>
> Cheers,
> -Barry
>
>
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-- 
--Guido van Rossum (python.org/~guido)
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