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Hi folks,
for 10.2 release, we have switched to Python 2.5. It's quite a big
change, so here's an assorted list of changes and things to look out for
while migrating.
toc:
1. pure Python apps and modules
2. C extensions and apps interfacing with Python
3. migrating packages - changes of the standard library
1. pure Python apps and modules
Pure Python modules should be largely unaffected, as the
majority of changes is backwards compatible. But, be sure to read
through the list of changes [1]. Just in case.
2. C extensions and apps interfacing with Python
Most of C extension modules will suffer from various problems on 64bit
platforms, because of transition to 64bit indices. To sum it up, Python
now uses a different type, Py_ssize_t instead of int, for indexing and
measuring strings, lists, tuples and dictionaries. Py_ssize_t is the
same size as int on 32bit platforms, but it is bigger on 64bits. The
change is described in great detail at [2], I'll just list a few
guidelines to fix the packages.
First and foremost, it's absolutely necessary to fix function calls that
use Py_ssize_t as output arguments. Most common are
PyString_AsStringAndSize and PyDict_Next, but there are quite a few others.
Second, when defining new Python types from C, you need to change
certain function signatures: intargfunc becomes ssizeargfunc and must
take Py_ssize_t argument, similarly with intintargfunc and other int*funcs.
Then there are some lesser tasks - some functions (Py*_Size) return
Py_ssize_t, so you should either store it in a proper variable, or check
for integer overflow; many others take Py_ssize_t as input...
None of this is really necessary to fix, though - if left as is, the
extension will work, only it won't be able to access elements beyond int
limit.
A script [3] can be used to find problems in the extension modules. It
also contains lists of affected functions, and provides a bit of
interesting insight. It's a must-read for everybody who is going to
tamper with C extensions. (I didn't read it at first, and i've regretted
it deeply.)
There is one more thing that can cause problems: due to a change in
Python internal memory allocation, PyMem_* and PyObject_* allocation
families are no longer interchangeable.
That means that when deallocating a custom type, you need to use
PyObject_Del insteand of PyMem_DEL, as many modules now do.
If an app or extension is crashing on "invalid free()", it's almost
certainly caused by this. Check your code, looking for functions like
Py*_Dealloc.
3. migrating packages - changes of the standard library
Good news everyone, distutils are back in the core python package.
Bad news is that you still need python-devel to do "python setup.py
install", because it includes the Makefile necessary for installation.
As of now, this is intentional, but it will probably change before 10.3.
On this place I'd like to remind everyone of two things:
- - since 10.1 distutils install by default into /usr/local. You want to
add --prefix=%{_prefix} to the install command in specfile
- - Python packages, even pure Python, are not noarch. This is because of
/usr/lib vs. /usr/lib64 discrepancy. On 64bit systems, /usr/lib is not
in the search path (and yes, this is intentional, because of C
extensions), so packages installed there will not work.
We'd like to solve this issue somehow, but FHS is limiting, because it
doesn't recognize arch-independent library code.
In other news, Python 2.5 brings us new additions to the standard library.
Part of the ElementTree module is now included. The module has a
different name, but many packages out there can already use it. It's
inside python-xml subpackate.
Another welcome addition is the Sqlite3 module. (sadly it didn't work in
intial release, we are now shipping an update) It's in the core package,
you don't need to add any dependencies.
We also have ctypes, hashlib and wsigref. You can read more about them
in [4].
If you have any problems with the transition, feel free to contact me.
Regards
Jan Matejek
[1] http://docs.python.org/whatsnew/other-lang.html
[2] http://www.python.org/dev/peps/pep-0353/
[3] http://svn.effbot.python-hosting.com/stuff/sandbox/python/ssizecheck.py
[4] http://docs.python.org/whatsnew/modules.html
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