> yes i know it's related to search path, but i don't know how to set it in a > practical way (beside hard coding). > my concern is, if i want to create a custom module/library, i don't know > what py file will import it and where the working directory should be.
Regarding where the current working directory is -- on Linux your right, you probably don't know where it is going to be. On Windows -- you can pretty much demand that users set up the launcher so that your python program is opened in a specific location -- typically the root directory of the installed package. So in the windows situation -- if all your components are in that package directory you can access everything via relative roots. Linux is not so easy -- I'll get to that. On the other hand, if your installing a general directory library module that your going to use from a variety of other programs, then you need to have the installer setup things so other applications can find it. The standard way to do this is to use the distutils package that is part of the python distribution to install these modules in a standard location which should already be in the search path. If you don't want to do that you have to do something special: on windows create a registry entry that can be accessed and looked up probably, or setup the default python path for your system (or user) to include the extra directories, or like GNOME does on Linux -- create a script in the executable search path that your program or installer can run -- and have it return the path you need. So on the application side, you'd find out the location of the library as described above and set sys.path. You can either do this at launch time in your main program -- or you can have the installer hard code it at the top of the main program. This is not really any different then for example using shared libraries. You either need to install all of your modules in the search path to start with or you need to modify the search path by some method. There is one more thought -- if you want to find out where the python module is in the file system -- there are sometimes ways to do this -- I've never done this but I have some notes somewhere about this. This might also be helpful in finding directories for example. If your interested in this -- maybe someone else here can remember? > But if i put a set of classes in a py file as a module, will it increase > the dependency of each class? > back to my example, of course, i can put BaseA and ClassA together in one py > file. what should i do when i need to add one more class later, "ClassB", > which also extend BaseA. Put it into the same file or in a new file? if put > in in the same file, i think it should difficult to maintain versioning. Versioning -- hmm. Well I think it depends. If ClassB is intended to be a general capability that you want to add to to moduleA (the module with BaseA and ClassA), then add it to moduleA but make the module upwardly compatible. If you want to track versions, then just keep old version snapshots if you need to or use something like CVS to do it for you. I'm pretty basic so I keep old copies but try to make my general libraries upwardly compatible if possible. Of course on the other hand, if the new class classB has a special function then I'd either create a new module, or I'd just include it into my main program module, or some other application module. To merge the functions just import what you need into that module. I for example often use "from mymodule import *" which imports everything rather than the limited imports you used -- nothing wrong with either, just a matter of taste. I also often use "import" and write the full module name when I reference things too. The point is -- I personally think one should look at modules as being collections of functions, classes, and other constructs that form librararies rather than putting each class and function in a separate module. Thanks, Rob -- http://mail.python.org/mailman/listinfo/python-list
