Imports in Packages

[Bruno Desthuilliers]

tjhnson at gmail.com a écrit :
> While working within a package...what is the 'best practice' way to do
> your imports.
> 
> a/__init__.py
> a/one.py
> a/two.py
> a/b/__init__.py
> a/b/cat.py
> a/b/dog.py
> a/c/cow.py
> Suppose I am working in a/c/cow.py and I need something from a/b/
> dog.py.  If a/b/__init__.py contains what I need from dog.py, should I
> do:
> 
> "from a.b import desiredfunction"
> 
> or
> 
> "from a.b.dog import desiredfunction"

What would be the point of exposing desiredfunction in a/b/__init__ if 
you still import it from a/b/dog ?-)

> What are your reasons for preferring one over the other (performance,
> readability, portability)? 

What about encapsulation of the package's internal organisation ?

(snip)
> I know that
> 
> 
>>>>from math import cos
>>>>x = cos(3)
> 
> 
> is preferred for performance reasons over
> 
> 
>>>>import math
>>>>x = math.cos(3)
> 
> because of the required lookup. 

If you only use it once, it won't make such a difference wrt/ lookup 
time. The "make names local" trick is mostly useful for tight loops in 
functions. Else, better to go for readability and favor the first form 
IMHO - at least you don't wonder where this 'cos' stuff come from !-)

> Does this mean that that I should
> import as far down as possible as well?  For example, "from a.b.c.mod
> import func"  versus  "from a import fun".

This won't save anything wrt/ lookup. And I stronly suggest that you 
read more about namespaces and lookup rules in Python.