How to structure packages

[Peter Otten]

bclark76 wrote:

> I'm learning python, and was playing with structuring packages.

If you are coming from Jave you have to unlearn a thing or two.
 
> Basically I want to have a package called mypackage that defines a
> number of classes and functions.

> I'm trying to follow the rule that every file defines only one class.
> I could define MyClass in __init__.py, but then what if I wanted to
> define more classes in the mypackage package? My one class per file
> rule goes out the window.
> 
> Is this rule wrongheaded, 

Yes. 

> or is there another way to do this?

I recommend that you always start out with a module. Once that becomes 
unwieldy you can convert it into a package. Let's assume that

mystuff.py

contains a MyClass that you want to move into a separate file. You get the 
following files:

mystuff
    __init__.py
    descriptivename.py # MyClass here

Note that all filenames are lowercase. If you add the line

from .descriptivename import MyClass

to __init__.py you can continue to import and use MyClass with the statement

from mystuff import MyClass
m = MyClass()

or

import mystuff
m = mystuff.MyClass()

The disadvantage is of course that mystuff.descriptivename will always be 
imported, even if you don't need the part of the mystuff package defined 
there.

You may also have a look into unittest as an example of a module that was 
recently converted into a package. Classes and functions are grouped into 
submodules by their functionality rather than employing Java's mechanical 
one-class-per-file pattern.