Web2Py Working Directory

Question

Well I want to use WEb2Py because it's pretty nice.. I just need to change the working directory to the directory where all my modules/libraries/apps are so i can use them. I want to be able to import my real program when I use the web2py interface/applications. I need to do this instead of putting all my apps and stuff inside the Web2Py folder... I'm trying to give my program a web frontend without putting the program in the Web2Py folder.. Sorry if this is hard to understand .

Answer 1

os.chdir lets you change the OS's working directory, but for your purposes (enabling imports of a bunch of modules &c which are constrained to live in some strange place) it seems better to add the needed directories to sys.path instead.

Answer 2

In any multi-threaded Python program (and not only Python) you should not use os.chdir and you should not change sys.path when you have more than one thread running. It is not safe because it affects other threads. Moreover you should not sys.path.append() in a loop because it may explode.

All web frameworks are multi-threaded and requests are executed in a loop. Some web frameworks do not allow you to install/un-install applications without restarting the web server and therefore IF os.chdir/sys.path.append are only executed at startup then there is no problem.

In web2py we want to be able to install/uninstall applications without restarting the web server. We want apps to be very dynamical (for example define models based on information provided with the http request). We want each app to have its own models folder and we want complete separation between apps so that if two apps need to different versions of the same module, they do not conflict with each other, so we provide APIs to do so (request.folder, local_import).

You can still use the normal os.chdir and sys.path.append but you should do it outside threads (and this is not a web2py specific issue). You can use import anywhere you like as you would in any other Python program.

I strongly suggest moving this discussion to the web2py mailing list.

Answer 3

I had to do this very thing. I have few modules that I wanted to use from my controllers. If you want to be able to use the code that resides in the modules directory in the controller, you can use:

# use this in your controller code
impname = local_import('module_in_modules', reload=True)
# reload true  will ensure that it will re load whenever
# there are changes to the module

Jay