[Chicago] import question

Massimo Di Pierro mdipierro at cs.depaul.edu
Wed Jan 23 18:34:32 CET 2008

As I explained in the original post, editing sys.path that may create  
problems with py2exe and py2app.

When people write code, they should not assume that their modules are  
going to be installed in site-packages or in a location in sys.path.


On Jan 23, 2008, at 11:10 AM, Kumar McMillan wrote:

> On Jan 23, 2008 10:07 AM, Massimo Di Pierro  
> <mdipierro at cs.depaul.edu> wrote:
>> if I import it it works. But in web2py apps, ideally the individual
>> applications should carry packages with themselves because they are
>> not supposed to have dependencies. It is a long story.
>> installing is what I do not want to do.
> if you are trying to package 3rd party deps with an app, it is my
> humble opinion that you should alter sys.path instead of turning them
> into submodules.  That is, mimic "installation."  This will make
> future maintenance of updating the dependency *much* easier.  I would
> propose a directory structure that mimics site-packages instead of a
> myapp.contrib approach.  I think django can mostly get away with a
> contrib submodule because these are modules that were written to live
> specifically in django.contrib.  What you are doing is different, you
> are distributing copies of modules that were written to be used as a
> global python modules.  Here is a possible structure :
> frozen/
>     openid/
>         __init__.py
>     simplejson/
>         __init__.py
> myapp/
>     __init__.py
>     something
>         __init__.py
> the tricky part is altering sys.path at the right time but if you
> already have a standalone app then there should be one point of entry
> into that app already.  Call it run_my_app.py and have it look
> something like:
> #!/auto/generated/path/to/python
> import sys
> sys.path = [
>     '/auto/generated/path/to/frozen'
> ] + sys.path
> from myapp import main
> main()
> ... and an analogous test_my_app.py script as well.
> Then, anytime your app does "import simplejson" or "import openid" it
> will get the *frozen* version that you want to package with your app,
> not a global one from site-packages.  You ever want to update
> simplejson?  No problem!  Just replace the one in frozen.  This would
> be a more maintainable use of 3rd party python modules.  Of course,
> the contrib submodule approach would work if *every* single 3rd party
> package supported relative imports.  This will only happen when it is
> an acceptable time to drop 2.4 support, which is a long way off.
> Maybe our children will live through that era :)
> BTW ... I think bundling dependencies is a smart idea and I wish it
> were a bit easier to do in Python.  Imagine a production server where
> you have 10 apps deployed and you want to upgrade a global package;
> this is a regression test nightmare that no matter how talented your
> QA team is will be very very hard to get right.  At my company we have
> a tool that uses setuptools to make a local package of eggs per
> application but it's still a hack of sorts and is prone to breakage
> when setuptools changes.
> Of course, the industry standard solution to this (Amazon does this I
> believe) is to use vmware to create one single "OS" per application,
> for ultimate isolation.  If you have that luxury then this is the way
> to go.
> Kumar
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