# 19 Build and C API Changes

Changes to Python's build process and to the C API include:

- The C-level interface to the garbage collector has been changed to make it easier to write extension types that support garbage collection and to debug misuses of the functions. Various functions have slightly different semantics, so a bunch of functions had to be renamed. Extensions that use the old API will still compile but will not participate in garbage collection, so updating them for 2.3 should be considered fairly high priority.

  To upgrade an extension module to the new API, perform the following steps:

  - Rename `Py_TPFLAGS_GC` to `PyTPFLAGS_HAVE_GC`.

  - Use `PyObject_GC_New` or `PyObject_GC_NewVar` to allocate objects, and `PyObject_GC_Del` to deallocate them.

  - Rename `PyObject_GC_Init` to `PyObject_GC_Track` and `PyObject_GC_Fini` to `PyObject_GC_UnTrack`.

  - Remove `PyGC_HEAD_SIZE` from object size calculations.

  - Remove calls to `PyObject_AS_GC` and `PyObject_FROM_GC`.

- The cycle detection implementation used by the garbage collection has proven to be stable, so it's now been made mandatory. You can no longer compile Python without it, and the --with-cycle-gc switch to configure has been removed.

- Python can now optionally be built as a shared library (libpython2.3.so) by supplying --enable-shared when running Python's configure script. (Contributed by Ondrej Palkovsky.)

- The DL_EXPORT and DL_IMPORT macros are now deprecated. Initialization functions for Python extension modules should now be declared using the new macro PyMODINIT_FUNC, while the Python core will generally use the PyAPI_FUNC and PyAPI_DATA macros.

- The interpreter can be compiled without any docstrings for the built-in functions and modules by supplying --without-doc-strings to the configure script. This makes the Python executable about 10% smaller, but will also mean that you can't get help for Python's built-ins. (Contributed by Gustavo Niemeyer.)

- The `PyArg_NoArgs()` macro is now deprecated, and code that uses it should be changed. For Python 2.2 and later, the method definition table can specify the `METH_NOARGS` flag, signalling that there are no arguments, and the argument checking can then be removed. If compatibility with pre-2.2 versions of Python is important, the code could use `PyArg_ParseTuple(args, "")` instead, but this will be slower than using `METH_NOARGS`.

- A new function, `PyObject_DelItemString(mapping, char *key)` was added as shorthand for `PyObject_DelItem(mapping, PyString_New(key))`.

- File objects now manage their internal string buffer differently, increasing it exponentially when needed. This results in the benchmark tests in Lib/test/test_bufio.py speeding up considerably (from 57 seconds to 1.7 seconds, according to one measurement).

- It's now possible to define class and static methods for a C extension type by setting either the `METH_CLASS` or `METH_STATIC` flags in a method's `PyMethodDef` structure.

- Python now includes a copy of the Expat XML parser's source code, removing any dependence on a system version or local installation of Expat.

- If you dynamically allocate type objects in your extension, you should be aware of a change in the rules relating to the `__module__` and `__name__` attributes. In summary, you will want to ensure the type's dictionary contains a `'__module__'` key; making the module name the part of the type name leading up to the final period will no longer have the desired effect. For more detail, read the API reference documentation or the source.

## 19.1 Port-Specific Changes

Support for a port to IBM's OS/2 using the EMX runtime environment was merged into the main Python source tree. EMX is a POSIX emulation layer over the OS/2 system APIs. The Python port for EMX tries to support all the POSIX-like capability exposed by the EMX runtime, and mostly succeeds; `fork()` and `fcntl()` are restricted by the limitations of the underlying emulation layer. The standard OS/2 port, which uses IBM's Visual Age compiler, also gained support for case-sensitive import semantics as part of the integration of the EMX port into CVS. (Contributed by Andrew MacIntyre.)

On MacOS, most toolbox modules have been weaklinked to improve backward compatibility. This means that modules will no longer fail to load if a single routine is missing on the curent OS version. Instead calling the missing routine will raise an exception. (Contributed by Jack Jansen.)

The RPM spec files, found in the Misc/RPM/ directory in the Python source distribution, were updated for 2.3. (Contributed by Sean Reifschneider.)

Other new platforms now supported by Python include AtheOS (http://www.atheos.cx/), GNU/Hurd, and OpenVMS.