Packaging question

Peter Otten __peter__ at web.de
Fri Jul 2 04:22:31 EDT 2010


snorble wrote:

> My question is, why do the modules bar and foo show up in mypack's
> dir()? I intend for Foo (the class foo.Foo) and Bar (the class
> bar.Bar) to be there, but was not sure about the modules foo and bar.

> $ ls mypack/*.py
> bar.py
> foo.py
> __init__.py
> 
> $ cat mypack/__init__.py
> from foo import Foo
> from bar import Bar
> 
> $ python
> Python 2.6.5 (r265:79096, Mar 19 2010, 21:48:26) [MSC v.1500 32 bit
> (Intel)] on win32
> Type "help", "copyright", "credits" or "license" for more information.
>>>> import mypack
>>>> dir(mypack)
> ['Bar', 'Foo', '__builtins__', '__doc__', '__file__', '__name__',
> '__package__', '__path__', 'bar', 'foo']


How is Python to know that you won't perform an

import mypack.foo

afterwards? After this statement foo must be an attribute of mypack. But 
when mypack.foo has been imported before this just performs

mypack = sys.modules["mypack"]

If the foo attribute weren't added by 

from foo import Foo

the caching mechanism would not work. While

import mypack.foo

might also have been implemented as

mypack = sys.modules["mypack"]
if not hasattr(mypack", "foo"):
    mypack.foo = sys.modules["mypack.foo"]
 
I think that would have been a solution to a non-problem. If you're sure you 
don't need to access mypack.foo directly you can add

del foo

to mypack/__init__.py, but don't complain when you get bitten by

>>> import mypack.foo
>>> mypack.foo
Traceback (most recent call last):
  File "<stdin>", line 1, in <module>
AttributeError: 'module' object has no attribute 'foo'

> My big picture intention is to create smaller modules, but more of
> them (like I am used to doing with C++), and then use a package to
> organize the namespace so I'm not typing out excessively long names
> and making the code less readable. Is that a reasonable approach to
> developing Python programs?

I like to put related classes and functions into a single file. As a rule of 
thumb, when a class needs a file of its own the class is too big...

Peter




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