Possibilities for Python classes organized across files? [closed]

A Python file is called a "module" and it's one way to organize your software so that it makes "sense". Another is a directory, called a "package".

A module is a distinct thing that may have one or two dozen closely-related classes. The trick is that a module is something you'll import, and you need that import to be perfectly sensible to people who will read, maintain and extend your software.

The rule is this: a module is the unit of reuse.

You can't easily reuse a single class. You should be able to reuse a module without any difficulties. Everything in your library (and everything you download and add) is either a module or a package of modules.

For example, you're working on something that reads spreadsheets, does some calculations and loads the results into a database. What do you want your main program to look like?

from ssReader import Reader
from theCalcs import ACalc, AnotherCalc
from theDB import Loader

def main( sourceFileName ):
    rdr= Reader( sourceFileName )
    c1= ACalc( options )
    c2= AnotherCalc( options )
    ldr= Loader( parameters )
    for myObj in rdr.readAll():
        c1.thisOp( myObj )
        c2.thatOp( myObj )
        ldr.laod( myObj )

Think of the import as the way to organize your code in concepts or chunks. Exactly how many classes are in each import doesn't matter. What matters is the overall organization that you're portraying with your import statements.

Since there is no artificial limit, it really depends on what's comprehensible. If you have a bunch of fairly short, simple classes that are logically grouped together, toss in a bunch of 'em. If you have big, complex classes or classes that don't make sense as a group, go one file per class. Or pick something in between. Refactor as things change.

I happen to like the Java model for the following reason. Placing each class in an individual file promotes reuse by making classes easier to see when browsing the source code. If you have a bunch of classes grouped into a single file, it may not be obvious to other developers that there are classes there that can be reused simply by browsing the project's directory structure. Thus, if you think that your class can possibly be reused, I would put it in its own file.