Python Testing with pytest

Creating an Installable Package

Let’s make this code a package by adding an __init__.py and putting the __init__.py file and module in a directory with a package name:

	$ tree some_package_proj/
	some_package_proj/
	├── setup.py
	└── src
	└── some_package
	├── __init__.py
	└── some_module.py

The content of some_module.py doesn’t change. The __init__.py needs to be written to expose the module functionality to the outside world through the package namespace. There are lots of choices for this. I recommend skimming the two sections of the Python documentation^[54] that cover this topic.

If we do something like this in __init__.py:

import some_package.some_module

the client code will have to specify some_module:

	import some_package
	some_package.some_module.some_func()

However, I’m thinking that some_module.py is really our API for the package, and we want everything in it to be exposed to the package level. Therefore, we’ll use this form:

appendices/packaging/some_package_proj/src/some_package/__init__.py

from some_package.some_module import *

Now the client code can do this instead:

	import some_package
	some_package.some_func()

We also have to change the setup.py file, but not much:

appendices/packaging/some_package_proj/setup.py

	from setuptools import setup, find_packages

	setup(
	name='some_package',
	packages=find_packages(where='src'),
	package_dir={'': 'src'},
	)

Instead of using py_modules, we specify packages.

This is now installable:

	$ cd /path/to/code/appendices/packaging
	$ pip install ./some_package_proj/
	Processing ./some_package_proj
	Installing collected packages: some-package
	Running setup.py install for some-package ... done
	Successfully installed some-package-0.0.0

and usable:

	$ python
	Python 3.6.1 (v3.6.1:69c0db5050, Mar 21 2017, 01:21:04)
	[GCC 4.2.1 (Apple Inc. build 5666) (dot 3)] on darwin
	Type "help", "copyright", "credits" or "license" for more information.
	>>> from some_package import some_func
	>>> some_func()
	42

Our project is now installable and in a structure that’s easy to build on. You can add a tests directory at the same level of src to add our tests if you want. However, the setup.py file is still missing some metadata needed to create a proper source distribution or wheel. It’s just a little bit more work to make that possible.