En Tue, 24 Mar 2009 12:49:08 -0300, Istvan Albert
<istvan.alb...@gmail.com> escribió:
On Mar 23, 10:16 am, CinnamonDonkey <cinnamondon...@googlemail.com>
wrote:
I'm fairly new to Python so I still have a lot to learn. But I'd like
to know how to correectly use relative imports.
Relative imports are *fundamentally* broken in python. You will soon
see that code using relative import will break if you attempt to run
the module on its own. Yes, it is mindboggling!
How import works in general is hard to grasp -- the semantics are rather
complicated, partly because the import system has grown patch over patch
over the years, and because it's mostly underdocumented.
But I would not say that relative imports are "fundamentally broken" --
they're one of the best improvements to the import system!
Why is it so you ask? It is one of those issue that would be trivial
to implement correctly (it is relative to the current file location,
duh!!!), would be tremendously useful yet for some reason it is
controversial with those who would need to implement it.
A module doesn't *have* to reside in the filesystem - so in the general
case, there is no such thing as "current file location". Packages provide
such hierarchical disposition - and relative imports work with packages
only.
It looks like they think that the expected mode of operation would
greatly confuse the 'rest' of us. So that is the reason you end up
with a broken implementation that is worse than not having it at all.
All I can do is recommend that you avoid relative imports.
I'd recommend the oposite - use relative (intra-package) imports when
possible. Explicit is better than implicit - and starting with 2.7 -when
"absolute" import semantics will be enabled by default- you'll *have* to
use relative imports inside a package, or fail.
The easiest way around the issue is to create a module named
pathfix.py like the one below and import it in all of your modules.
This is the only way to fix this issue in a way that does not come
back and bite you, it is ugly, you are repeating yourself in multiple
places, but it is still better than the alternative.
"import it in all of your modules"?
Did you know, once a module is imported by the first time, subsequent
imports simply return the same module instance? The initialization code is
not executed again.
import os, sys
def path_join(*args):
return os.path.abspath(os.path.join(*args))
# adds base directory to import path to allow relative imports
__currdir = os.path.dirname( __file__ )
__basedir = path_join(__currdir, '..' )
if __basedir not in sys.path:
sys.path.append( __basedir )
I don't understand, how is this supposed to help relative imports?
Bindly inserting directories into sys.path can easily confuse the import
system (and you!)
--
Gabriel Genellina
--
http://mail.python.org/mailman/listinfo/python-list
