python/serial broken in OSX lion / launchd

I have a launchd entry that worked with OSX 10.6 but that fails with 10.7. It uses python, and it pro开发者_如何学运维duces an error whilst trying to import serial. I don't quite understand this, because I've re-downloaded pyserial-2.5 and re-installed it with sudo. (In desperation, I re-installed it for each of the many flavours of python on my machine.) As a test, I can enter python and do import serial without difficulties. Maybe there is a system path that is set up well for an interactive user, that is not set up for launched??

Can anyone suggest how I might diagnose the problem?

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The path you are appending:

/Library/Frameworks/Python.framework/Versions/2.7/lib/python2.7/site-packages

is the site-packages directory for a third-party, non-system Python, possibly installed using a python.org installer, and not that of the Apple-supplied system Python 2.7, which would be:

/Library/Python/2.7/site-packages

So most likely you are using the python.org Python to install pyserial but are launching the system Python under launchd. Check your shell PATH (echo $PATH), it probably has:

/Library/Frameworks/Python.framework/Versions/2.7/bin

in it. And try which python. If you want to use the python.org Python with your launchd plist, modify it to use an absolute path to the right Python, for instance:

/Library/Frameworks/Python.framework/Versions/2.7/bin/python

If you want to install pyserial with the system supplied Python, you can use an absolute path to it when doing the install:

/usr/bin/python2.7

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Some experimentation with python -S showed me that the sys.path was not set up properly, so I solved the issue by

import sys
sys.path.append('/Library/Frameworks/Python.framework/Versions/2.7/lib/python2.7/site-packages')
import serial

which I know is awkward, since it is so specific, but I guess I'll have to live with that, unless or until I can find a way to tell python where to find things, as it is being invoked from launched.

PS to anyone coming here later: the switch to OSX 10.7 (Lion) changed loads of things. Perhaps I had some initialization file somewhere, that I forgot about. If I find that, I'll try it that way, and post a further comment here.