Re: [Xen-devel] [PATCH for-next RFC 4/4] pygrub: make it build with python 3

[Wei Liu <wei.liu2@xxxxxxxxxx>]

On Tue, Mar 05, 2019 at 07:17:07PM +0100, Marek Marczykowski-Górecki wrote:
> On Tue, Mar 05, 2019 at 05:48:10PM +0000, Wei Liu wrote:
> > On Tue, Mar 05, 2019 at 05:42:07PM +0000, Andrew Cooper wrote:
> > > On 05/03/2019 16:42, Wei Liu wrote:
> > > > With the help of two porting guides and cpython source code:
> > > >
> > > > 1. Use PyUnicode to replace PyString counterparts.
> > > > 2. Use PyVarObject_HEAD_INIT and provide compatibility for 2.5 and
> > > >    earlier.
> > > > 3. Remove usage of Py_FindMethod.
> > > > 4. Use new module initialisation routine.
> > > >
> > > > For #3, Py_FindMethod was removed, yet an alternative wasn't
> > > > documented.  The code is the result of reverse-engineering cpython
> > > > commit 6116d4a1d1
> > > >
> > > > https://docs.python.org/3/howto/cporting.html
> > > > http://python3porting.com/cextensions.html
> > > >
> > > > Signed-off-by: Wei Liu <wei.liu2@xxxxxxxxxx>
> > > 
> > > Marek already made the tools/python/* libraries compatible with Py2 and 
> > > Py3
> > > 
> > > The following commits are the relevant ones:
> > > 
> > > * be6b316 - python: handle long type in scripts (2 years ago) <Marek 
> > > Marczykowski-Górecki>
> > > * e16c705 - python: adjust module initalization for Python3 (2 years ago) 
> > > <Marek Marczykowski-Górecki>
> > > * dd986cd - python: use PyLong_* for constructing 'int' type in Python3 
> > > (2 years ago) <Marek Marczykowski-Górecki>
> > > * 121d9d4 - python: use PyBytes/PyUnicode instead of PyString (2 years 
> > > ago) <Marek Marczykowski-Górecki>
> > > * 0c8981f - python: initialize specific fields of PyTypeObject (2 years 
> > > ago) <Marek Marczykowski-Górecki>
> > > * 7b1e5f7 - python: use Py_TYPE instead of looking directly into 
> > > PyObject_HEAD (2 years ago) <Marek Marczykowski-Górecki>
> > > * 96d1ee6 - python: drop tp_getattr implementation (2 years ago) <Marek 
> > > Marczykowski-Górecki>
> > > * 6b28df3 - python: check return value of PyErr_NewException (2 years 
> > > ago) <Marek Marczykowski-Górecki>
> > 
> > I knew.
> > 
> > > 
> > > Which in particular handle strings differently in the Py2 case.
> > 
> > 
> > I am not sure his changes for the string APIs are correct -- they seem
> > to deviate from the official porting guide. But hey, I don't use these
> > bindings myself, so he probably knows better.
> 
> That was intentional, because in py2 str type is the same as bytes
> types, and in fact some of those str should really be bytes. It's in the
> commit message:
> 
>     python: use PyBytes/PyUnicode instead of PyString
>     
>     In Python2 PyBytes is the same as PyString, but in Python3 PyString is
>     gone and 'str' is really PyUnicode in C-API.
>     When handling arbitrary data, use PyBytes - which is the right thing to
>     do in Python3, and pose no API change in Python2. When handling
>     xenstore paths and transaction ids, which have well defined format, use
>     PyUnicode - to ease API usage - no need to prefix all xenstore paths
>     with 'b' when migrating scripts to Python3.
> 
> I'm not sure if the same reasoning applies to pygrub, but I guess it
> may. For example fsimage_file_read sounds like handling binary data, not
> really UTF-8 strings. Using PyUnicode for arbitrary binary data may lead
> to various UnicodeDecodeErrors.

Good point. Let me dig into this a bit more. Frankly I trust you more
than I trust myself on this matter. :-)

Wei.

> 
> -- 
> Best Regards,
> Marek Marczykowski-Górecki
> Invisible Things Lab
> A: Because it messes up the order in which people normally read text.
> Q: Why is top-posting such a bad thing?



_______________________________________________
Xen-devel mailing list
Xen-devel@xxxxxxxxxxxxxxxxxxxx
https://lists.xenproject.org/mailman/listinfo/xen-devel