# Listing an optional Python dependency in setup.py

I have a small project that requires a third-party module that's rarely updated (once every other year or so) and not maintained by any package management system. The context, here, is cognitive science & research, the third party module is for linking proprietary hardware to custom scripting, in the house project, potentially, may end up seeing wider (eventually open source) use within cog. psych so I want to plan for distribution.

Can anyone poke holes in or thumbs up this approach:

#!/usr/bin/env python

from distutils.core import setup

try:
import third_party_package
install_packages = ['in_house_package']
except ImportError:
print "Warning: 'third_party_package' not found in PYTHON_PATH, installing version in_house_package v. <VERSION>"
install_packages = ['in_house_package', 'in_house_package.third_party_package']

setup(
name='InHousePackage',
version = '0.1',
description = 'A framework for building psychological experiments in Python',
author = 'me',
url = 'a local git',
packages=install_packages,
requires = ['numpy']
)

• Do you have any plans of moving to python3 in the future? – shuttle87 Dec 13 '14 at 23:04
• For this project, no, alas; the third_party_package is critical and will, almost certainly, never be updated to Python 3. – Jonline Dec 15 '14 at 13:42

1. The error message looks wrong to me.

This is what the logic looks like to me:

if (third party package is installed):
install(in-house package)
else:
install(in-house package)
install(in-house variant of third-party package)


but the printed warning tells me that the in-house package isn’t installed. Shouldn’t it tell me the third-party package isn’t installed?

2. An ImportError doesn’t necessarily mean a module isn’t installed.

It just indicates any error when the module was imported. For example, if I have a file foo.py that contains:

import bar


and no module bar.py, I get an ImportError when trying to import foo, even though the foo file exists:

>>> import foo
Traceback (most recent call last):
File "<stdin>", line 1, in <module>
File "foo.py", line 1, in <module>
import bar
ImportError: No module named bar


You can jump through hoops with import tools, or check the error message of the ImportError. That may or may not be something worth worrying about; just remember that this edge case is there.

3. Trivial nitpicks.

• I’m sure this is just an artefact of posting on CR, and it isn’t actually called in_house_package, but you’ve misspelt it in the error message.
• When specifying keyword arguments to a function (such as setup()), it’s common to omit the spaces around the equals sign.