ImportError: No module named 'util'

Question

I know that there are many variations of this question, but I could not find one like mine. When I try to import the module illustris_python I get the error ImportError: No module named 'util' The module util is in the directory below the module snapshot.py that needs it so I am confused as to why python sees one module , but not the other. I have included the import call as well as traceback below.

Python 3.4.3 (v3.4.3:9b73f1c3e601, Feb 24 2015, 22:44:40) [MSC v.1600 64 bit (AMD64)]
Type "copyright", "credits" or "license" for more information.

IPython 3.0.0 -- An enhanced Interactive Python.
?         -> Introduction and overview of IPython's features.
%quickref -> Quick reference.
help      -> Python's own help system.
object?   -> Details about 'object', use 'object??' for extra details.
%guiref   -> A brief reference about the graphical user interface.

In [1]: import illustris_python as il
Traceback (most recent call last):

  File "<ipython-input-1-ff06d24b4811>", line 1, in <module>
    import illustris_python as il

  File "C:\WinPython-64bit-3.4.3.2\python-3.4.3.amd64\lib\site-     packages\illustris_python\__init__.py", line 3, in <module>
    from . import *

  File "C:\WinPython-64bit-3.4.3.2\python-3.4.3.amd64\lib\site- packages\illustris_python\snapshot.py", line 6, in <module>
    from util import partTypeNum

ImportError: No module named 'util'


In [2]: 

Solution

Looking at the BitBucket repo, I'm pretty sure the problem is that this code is Python 2.x-only. Someone's done some work to clean it up for an eventual port, but there's still more to be done.

This particular error is near the top of snapshot.py:

from util import partTypeNum

In Python 2.6, this is a relative import (it's "deprecated" by PEP 328, but I'm pretty sure you don't actually get the warning by default…), so it first looks in the same package as snapshot.py, where it finds a util.py, before looking through your sys.path.

In Python 3.4, it's an absolute import, so it just looks in your sys.path (well, it calls your top-level module finders, but usually that means looking in your sys.path), and there is no util.py there.

If you're trying to finish porting this sample code to 3.x yourself, just change it to an explicit relative import:

from .util import partTypeNum