On Jan 04, 2011, at 07:30 AM, Robert Collins wrote: >It really does look like having better upstream facilities would make >this a no-brainer for us; what I'd like to achieve though is something >that /works/ for the existing python platform - for 2.7 which will be >around a good long time, and then we'll have plenty of data to discuss >with upstream.
Let's assume you can work out the distro-specific issues (e.g. how to name the packages so that you can install wadllib1 and wadllib2 side-by side). What should work in Python would be to use .pth files. http://docs.python.org/library/site.html For example, let's say you have the following directory layout: .../wadllib1/ wadllib/ __init__.py ... .../waddlib2/ wadllib/ __init__.py ... You can now install a wadllib.pth file that has the directory the version you want to use by default, e.g. .../wadllib.pth contains: wadllib2 If wadllib.pth lives in the system site directory (or use site directory, but let's ignore that), then when you 'import wadllib' you'd get version 2. If wadllib.pth does not live in the site directory, then you have to explicitly: import site site.addsitedir('/path/to/pth/files/') to get Python to read and process the pth. Also note that Debian/Ubuntu's site.py has been modified from upstream, e.g. to add the dist-packages directory. If you wanted something more dynamic, you could exploit a trick in .pth processing where any line that starts with 'import' gets executed. Zope packages exploit this; for example, when you have python-zope.interface installed, see /usr/share/pyshared/zope.interface-3.6.1-nspkg.pth Totally bogus strawman: .../wadllib.pth contains: import os, sys; p=os.environ.get('WADLLIBDIR'); (p not in sys.path) and sys.path.append(p) You could now do: WADLLIB=/path/to/version/you/want python -c 'import wadllib' I'm sure you can come up with a much better mechanism to decide how to dynamically locate the version you want. The important things to remember are that only lines that start with 'import' are executed, and you have to obviously have your selection criteria set before Python reads your .pth file, which in the case of those in the system site directory is at Python start up time (unless you use python -S). I hope that helps. It's the best I could come up with that works with current Python. You still have to figure out the Debian packaging issues. -Barry
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