non-standard module location (again)

[Steven D'Aprano]

On Fri, 21 Oct 2011 07:05:32 -0700, Shane wrote:

> Need to refine a question I asked earlier. If I have a module,
> 
> |--  foo
> |-------|
> |-------|---bar
> |-------|-------|
> |-------|-------|---__init__.py
> 
> then I can say import foo.bar

No you can't, not the way you have listed it. As shown, foo is just a 
directory, so "import foo" will fail. However, "import bar" may work, 
provided foo/bar is in the module search path.

Perhaps you mean you have a package, with a sub-package:

foo/
+-- __init__.py
+-- bar/
... +-- __init__.py

Now you have TWO modules, foo and foo.bar, and you can "import foo.bar" 
successfully.


> But suppose I want to import foo.bar.stuff and stuff isn't located on
> under `bar' because it's user
> supplied code:
> 
> |- stuff                             <- I want this to be logically
> under foo.bar
> |-------|---__init__.py           <- even though it's not under bar in
> the computer's file system

This is not clear what you are trying to do. Please explain more clearly 
what your module layout is.

foo/
+-- __init__.py
+-- stuff.py
+-- bar/
... +-- __init__.py


Or:

stuff.py
foo/
+-- __init__.py
+-- bar/
... +-- __init__.py


But since stuff is supposed to be a plugin, the most obvious, sensible 
way to lay out the modules would be:

foo/
+-- __init__.py
+-- plugins/
... +-- __init__.py
... +-- stuff.py
+-- bar/
... +-- __init__.py


and then "import foo.plugins.stuff". Clear, simple and obvious.


> Now what: how to arrange to do command: import foo.bar.stuff

Why do you want to call it foo.bar.stuff when it isn't actually 
foo.bar.stuff? Anyone trying to debug this will hate you, when they try 
to find a module foo/bar/stuff.py and can't find it because it doesn't 
exist.

If you must play games with module locations, put this inside the 
foo/bar/__init__.py module:

import foo.plugins.stuff as stuff

and now you can say "import foo.bar.stuff". But why bother?

Of course, plugin discovery is still a problem, but that's still a 
problem no matter what you do. Best to use a well-tested plugin library 
instead of trying to invent your own.



-- 
Steven