Python Packages?

Question

Ok, I think whatever I'm doing wrong, it's probably blindingly obvious, but I can't figure it out. I've read and re-read the tutorial section on packages and the only thing I can figure is that this won't work because I'm executing it directly. Here's the directory setup:

eulerproject/
  __init__.py
  euler1.py
  euler2.py
  ...
  eulern.py
  tests/
    __init__.py
    testeulern.py

Here are the contents of testeuler12.py (the first test module I've written):

import unittest
from .. import euler12

class Euler12UnitTests(unittest.TestCase):


    def testtriangle(self):
        """
        Ensure that the triangle number generator returns the first 10
        triangle numbers.

        """
        self.seq = [1,3,6,10,15,21,28,36,45,55]
        self.generator = euler12.trianglegenerator()
        self.results = []
        while len(self.results) != 10:
            self.results.append(self.generator.next())
        self.assertEqual(self.seq, self.results)

    def testdivisors(self):
        """
        Ensure that the divisors function can properly factor the number 28.

        """
        self.number = 28
        self.answer = [1,2,4,7,14,28]
        self.assertEqual(self.answer, euler12.divisors(self.number))


if __name__ == '__main__':

    unittest.main()

Now, when I execute this from IDLE and from the command line while in the directory, I get the following error:

Traceback (most recent call last):
  File "C:\Documents and Settings\jbennet\My Documents\Python\eulerproject\tests\testeuler12.py", line 2, in <module>
    from .. import euler12
ValueError: Attempted relative import in non-package

I think the problem is that since I'm running it directly, I can't do relative imports (because __name__ changes, and my vague understanding of the packages description is that __name__ is part of how it tells what package it's in), but in that case what do you guys suggest for how to import the 'production' code stored 1 level up from the test code?

Answer 1

Generally you would have a directory, the name of which is your package name, somewhere on your PYTHONPATH. For example:

eulerproject/
    euler/
        __init__.py
        euler1.py
        ...
        tests/
            ...
    setup.py

Then, you can either install this systemwide, or make sure to set PYTHONPATH=/path/to/eulerproject/:$PYTHONPATH when invoking your script.

An absolute import like this will then work:

from euler import euler1

Edit:

According to the Python docs, "modules intended for use as the main module of a Python application should always use absolute imports." (Cite)

So a test harness like nose, mentioned by the other answer, works because it imports packages rather than running them from the command line.

If you want to do things by hand, your runnable script needs to be outside the package hierarchy, like this:

eulerproject/
    runtests.py
    euler/
        __init__.py
        euler1.py
        ...
        tests/
            __init__.py
           testeulern.py

Now, runtests.py can do from euler.tests.testeulern import TestCase and testeulern.py can do from .. import euler1

Answer 2

I had the same problem. I now use nose to run my tests, and relative imports are correctly handled.

Yeah, this whole relative import thing is confusing.