import in Python3.3

Steven D'Aprano steve+comp.lang.python at pearwood.info
Wed Mar 27 00:06:02 CET 2013


On Tue, 26 Mar 2013 08:37:00 -0700, rocky wrote:

> And again, I get the impression that for the use case asked about, there
> isn't much ambiguity. If I am in mypackage.foo and I want to access
> mypackage.collections I should be able to say something like that
> without ambiguity or that much inference or directory searching.

And you can: either explicitly say

import mypackage.collections

or use a relative import:

from . import collections

both of which only look inside mypackage.

> If
> mypackage.colletions is not found inside the same directory as
> mypackage.foo, often I DON'T WANT Python to helpfully go searching
> around other places for it which sys.path will do.

With both solutions above, Python will not.


> Instead what I
> probably want is Python to give me an error.
> 
> So again I come to import_relative,
> http://code.google.com/p/pyimport-relative/.  And again, I wish this
> package didn't have to exist.


I'm not convinced it does. I don't understand the problem you are trying 
to solve. "Provide relative imports" is not that problem, because the use-
case you give on the project page does not describe relative imports, as 
they are understood in Python terminology.

The error message you get gives the game away:

ValueError: Attempted relative import in non-package

In a stand-alone module, you can't do a relative import because there is 
no package structure, hence there is nothing to import relative to.

As I don't quite understand your use-case, I'm a shooting in the dark 
here, but it seems to me that you could fix this entire problem by simply 
using a package instead of a directory of stand-alone modules. A mere 
directory of stand-alone modules should be merely loosely coupled, no 
different from any other modules in sys.path. If your modules are tightly 
coupled, they should go in a package.

One thing which would make import manipulations much easier would be if 
import (and __import__) took an explicit search path, as opposed to 
operating on a system-wide global. E.g.

import module using this_path

would be nice.


-- 
Steven



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