On 22 October 2012 16:14, eryksun <eryk...@gmail.com> wrote: > On Mon, Oct 22, 2012 at 9:35 AM, Oscar Benjamin > <oscar.j.benja...@gmail.com> wrote: >> >> It is also sometimes useful to define a number of scripts that are in >> the same directory but share some code by importing one another. You >> need the if __name__ =="__main__" block for this. >> >> The problem that Devin is referring to only happens in certain odd >> situations where the script that you run ends up importing itself >> (perhaps indirectly). I have never personally had that problem though. > > Just to clarify that I'm following you, would you count the following > as a script importing itself 'indirectly'?
Yes. > Assume two modules in the same directory, mod1.py and mod2.py, can > both act as the main entry point, and both import each other (assume > no circular import problem). They both import each other. That is a circular import and it can create problems. My advice for this issue is not "avoid importable scripts" but rather "avoid circular imports" (a good idea anyway). > Then if mod1.py runs as __main__ and > imports mod2, and mod2.py imports mod1, there are 2 copies of the > classes and functions defined in mod1.py. For example, there's > __main__.MyError vs mod1.MyError. I agree that this would be problematic. However, if mod1.py and mod2.py both import each another then neither of them is really an independent script. There is no reason why any common code should not be moved into a third module to avoid the circular import. I have used importable scripts many times and never had this problem because I have never used them with circular imports. Typically the action of running the module as a script provides a command line interface that does some common but useful thing with the code in that same module (rather than code imported from other modules). An example from a recent project: I have a module that defines functions for interacting with a particular database. It can be imported by scripts that perform computations based on the contents of the database. It can also be run as a script in which case it provides a command line interface to query/export the contents of the database. This particular module does not import any other modules within the same project so it will never have the circular import problem. There are other importable scripts that depend on the database module but they also don't use circular imports. Oscar _______________________________________________ Tutor maillist - Tutor@python.org To unsubscribe or change subscription options: http://mail.python.org/mailman/listinfo/tutor
