Insanely Low-Level

The problem is that you cannot import modules from different (relative) paths in Python. Now sometimes it’s really a must. Like when you have a generic CPU module and then a subdirectory called ‘x86’ that wants to derive that CPU class and create a ‘x86CPU’.

So I tried to mess up with __import__ but without any luck. Then I said I just want to solve this problem, don’t care how far (ugly) I go. I started with execfile, which AFAIK isn’t exactly like import, but it’s good enough for me. execfile(“../cpu.py”) didn’t work, unforetunately. I then realized that the cpu.py file imports another file from its own directory and since the execfile doesn’t do some magic with the directories the import simply failed. Bammer. Next thing I did was to add the path of the CPU module to the sys.path and retried my attempt with a success. Although it works, I don’t like the directory separator which isn’t cross-platform. And yes I said it’s a temporary solution, but I’m still sensitive to it. Usually temporary hacks that work tend to stay there, as much as I don’t like this reproach…this is how things work usually, no?

So that one was solved, quite easily, but another one arised. In the original code (when all files used to be in the same directory) when import worked I always import the module name, and not the lot of it (import * from cpu – bad habit). So all my code is accessing the CPU module with ‘CPU.’ prefix, which is good, you know the source of everything you touch. The new problem is that since I moved to use execfile this prefix is ill now and I must get rid off it.

I thought about changing the globals dictionary to the name of the module I want to execfile() and then switch it back. But it becomes too nasty, and I’m not sure whether it would work anyway. My first attempt might be ok for some of you, alas, it’s still not good enough for me.

And I think my design with the files is ok, after all it makes sense. And yes, I know I (maybe?) should have put the files in site-packages directory and the import then would work well. However, I want the files to be in a specific directory out of Python reach (in a way).

Oh by the way, the code of my attempt is:

import os, sys
sys.path.append(os.getcwd()[:os.getcwd().rfind(os.sep)])
execfile(“..” + os.sep + “cpu.py”)

Ugly something, heh?

Ok I was just going to publish this post but I had to try another thing which really solved the issue. I managed to use __import__ well.

So now it looks like:

import os, sys
sys.path.append(os.getcwd()[:os.getcwd().rfind(os.sep)])
cpu = __import__(“cpu”)

This time it solves the second problem as well – the namespace (of the module)  issue. And yet we need the new path. Can we get rid off it?

This entry was posted on Wednesday, December 19th, 2007 at 8:33 pm and is filed under Python. You can follow any responses to this entry through the RSS 2.0 feed. You can leave a response, or trackback from your own site.