[Python-porting] main() -> Py_SetProgramName()

[M.-A. Lemburg]

On 05.12.2012 01:12, Barry Warsaw wrote:
> One gotcha with porting embedded Python 3 is the mismatch between main()'s
> signature and Py_SetProgramName() and PySys_SetArgv().
> 
> In Python 2, everything was easy.  You got char*'s from main() and could pass
> them directly to these two calls.  Not in Python 3, because they now take
> wchar_t*'s instead.  I get why these signatures have changed, but that doesn't
> make life very easy for porters.
>
> Take a look at main() in Modules/python.c to see the headaches Python itself
> goes through do the conversions.  I think we're doing a disservice to
> embedders not to provide convenience functions, alternative APIs, or at the
> very least code examples for helping them do the argument conversions.  This
> is not easy code, it's error prone, and folks shouldn't have to roll their own
> every time they need to do this.
> 
> Using the algorithm in main() is probably not the best recommendation either,
> because it uses non-public API methods such as _Py_char2wchar().  Perhaps
> these should be promoted to a public method, or we should add a method to get
> from main()'s char** to a wchar_t**.
> 
> For now, I've tried to use mbsrtowcs(), though I haven't done extensive
> testing on the code.  I think Python ultimately uses mbstowcs() down deep in
> its bowels.

There's also another issue with the approach, since changing the
**argv from within Python is no longer possible on non-Windows
platforms.

This doesn't only affect embedded uses of Python, but all other
uses as well, e.g. it's no longer possible to change the ps output
under Unix for daemons and the like.

I think that we should have APIs going from the original char **argv
to the Py_Main() wchar_t **argv one, as well as APIs that allow
changing or at least accessing the original char **argv from within
Python (on non-Windows platforms).

That said, I don't think this is going to happen in a patch level
release...

-- 
Marc-Andre Lemburg
eGenix.com

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