PyMaemo/Python 2.6 porting guide
Python 2.6 Porting Guide
Important: this document is still a draft. There are currently no planned dates for migration to 2.6, but it will be informed in advance on the maemo-developers and pymaemo-developers mailing lists, so that developers have some time to fix their packages.
This documents contains some general guidelines about how to port your Python application currently being used with Python 2.5 for working without problems with Python 2.6.
Introduction
Currently, Maemo 4.x (Diablo) has Python 2.5. Maemo 5 Beta (Fremantle) also has 2.5, but we are evaluating upgrading Fremantle to 2.6, so that developers can use the latest features, while keeping compatibility with Python 2.5. See the What’s New in Python 2.6 page for details.
This also means that we have no plans to migrate to Python 3.x in Fremantle. Using Python 2.6 is the best option because developers can use most 3.x features without breaking compatibility with Python 2.5.
One question might arise: why not have both 2.6 and 3.x, or even 2.5, 2.6 and 3.x? We have thought about this, the problem is, in the current mechanism used in Debian and Ubuntu (that we also use), the packages that install Python extensions need to be compiled for all supported versions, and all these versions are installed in a single package. This means that some packages will simply double or triple their size even if only one version is installed.
Besides, if we have two or three versions available in the repository, there is a possibility that some packages depend on e.g. 2.5 while others depend 3.x. So the user would need to have both versions installed in some cases.
For small devices as the Internet Tablets, saving space is also a high priority, so we decided to support a single version during the life cycle of the distribution.
FINISH ME
- Any paths that, for some reason, must have hardcoded "python2.5" or "site-packages" will have to be changed to "python2.6" and "dist-packages", as these are the ones used on Python 2.6.
- If you use distutils for building your package, you must pass the --install-layout=deb flag for "setup.py install" command inside debian/rules in order to install the files to the proper locations. If you're using CDBS for this task, use the variable DEB_PYTHON_INSTALL_ARGS_ALL for passing the flag, e.g.:
- DEB_PYTHON_INSTALL_ARGS_ALL = --no-compile -O0 --install-layout=deb
- If your application uses any python2.5 package as one of its dependencies in any Depends field, you should drop the version number and add the version as a requirement - as a example, python2.5 can be changed to python (>= 2.5) without problems. If this is not possible/desired, just change the dependencies to python2.6.
- Also, this would be a good time for your package to use dependencies that follow the new Debian Python Policy, if that's the case - the Policy states that Python packages must not have a fixed version number on its name (e.g. prefer python-xml instead of python2.6-xml).