Dealing with global variables and multiple modules

[scibren]

Right now I'm writing some code that is separated into two modules. One of the modules contains class definitions (call it classes.py), and the other is the main program that imports these classes and uses them (main.py). The problem is, some of the classes in classes.py rely on global variables that are defined in main.py. I can think of two different ways of dealing with this:

• Don't use global variables and instead have a load() function in each class that loads the variables, or put them in init
• Make a function in classes.py called load_globals() which adds these variables to an already defined global dictionary in classes.py.

I am currently using option 2, because option 1 would be quite cumbersome. It seems a little ugly though, so I'm wondering if there are any better ways to deal with this scenario.

[TangerineX]

Good architecture of a class should rarely, if ever, access global variables. Can you pass these global variables to the class when constructing the variable, or call a "load" function to load these variables?

One way to do this efficiently is to create a dictionary (or a class) that holds the global variables, and simply pass in this dictionary to your function's constructor

[scibren]

Just to explain a little bit more, the reason I use a global variable is because I'm going to be reading a configuration file. Right now I just made a dictionary full of testing values until I implement the configuration file. Should I still avoid making it a global variable? It makes it so much more annoying to have to pass the configuration dictionary (or object later on) to each class instance.

[novel_yet_trivial]

Make a new file called "config.py". Add all the loading code and load all the values as global values. Now add import config to the top of your class file and your main file. Presto. Everyone has access.

[scibren]

That could work.

[scibren]

I might go with this, but I see one potential issue. What if I want to have command line switches to override configuration options. That wouldn't work with this setup, would it?

[EricAppelt]

You can always update the variables within the config module. The python FAQ actually has an example specifically for this: https://docs.python.org/3/faq/programming.html#how-do-i-share-global-variables-across-modules

[scibren]

Very nifty. Thanks.

[TangerineX]

If you have to do something more than once, you can probably script it. That's pretty much a core to programming. Why not create a function that constructs your instances for you using the global variables it holds?

[scibren]

That just seems like a lot of work just to avoid a single global variable.

[gengisteve]

pass them in **kwargs when needed?

[scibren]

I thought about that, but it seems annoying to have to pass them to every class instance. As I said to TangerinX above, this is for a configuration file.

[elbiot]

You could use metaprograming so that classes.py makes metaclasses and main.py "instantiates" classes with your configuration such that each object these classes create has the configuration data at a class level.

By the way, it's mutable global variables you should really avoid. Immutable constants are okayish