Python Package 101

2015-08-22 ·

In order to distribute a Python application, you need to create a Python package by wrapping project directory with some additional files, specifing related elements e.g. resources, dependencies and finally releasing it.

Creating a Python Package

This is an example of a Pyhon package distribution file (named: setup.py).

from setuptools import setup

setup(
    name = 'zaiste',
    version = '0.1.0',
    description = 'A Python package example',
    author = 'Zaiste',
    long_description=open("README.txt").read(),
    author_email = 'oh@zaiste.net',
    url = 'https://github.com/zaiste/zaiste-py',
    packages=['zaiste'],
    include_package_data=True,
    install_requires=[
        # list of this package dependencies
    ],
    entry_points={
        'console_scripts': ['zaiste-cli=zaiste.cli:main'],
    }
)

In order to facilitate the tasks of distribution, Python distribution utilities toolset distutils was created by the Python core team. It is, however, preferable to use a 3rd party setuptools instead.

If you need to add extra non-Python files and directories e.g. static files or templates, you must explicitly specify them in the manifest file (MANIFEST.in) to be packaged along with adding include_package_data=True to the setup() function.

include README.rst
include docs/*.md
recursive-include templates *
recursive-include static *

Additionally, you can use packages that are properly arranged using setuptools, but aren’t published to PyPI; dependency_links= option is used for that:

setup(
    ...
    dependency_links=['http://github.com/zaiste/zaiste-py/tarball/master#egg=package-2.0']
    ...
)

You can now create a Python package for this project

python setup.py sdist

and install it locally

pip install .

The command above is similar to python setup.py install but:

  • it automatically downloads all dependencies
  • you can easily uninstall and update packages with a single command
  • pip will automatically search the Python Package Index (PyPi)
  • pip is bundled with Python (as of Python 2.7.9 / Python 3.4.0)

or install the package with a symlink (changes to the source files will be immediately available to other users of the package)

pip install -e .

Python package (and module) names should be in lowercase, unique on PyPI, with no hyphens (-) and prefereably no underscore (_) signs

zaiste/
    zaiste/
        __init__.py
    setup.py

Adding tests

Create a tests directory inside your module

zaiste/
    zaiste/
        __init__.py
        tests/
            __init__.py
            test_zaiste.py
    setup.py

and use unittest to write simple unit tests

from unittest import TestCase

import zaiste

class TestZaiste(TestCase):
    def test_is_string(self):
        s = zaiste.cli()
        self.assertTrue(isinstance(s, basestring))

You can use Nose to easily run those tests

$ pip install nose
$ nosetests

Nose integrates with setup.py

setup(
    ...
    test_suite='nose.collector',
    tests_require=['nose'],
)

so you can just do

python setup.py test

Adding Command Line Scripts

You can use scripts

setup(
    ...
    scripts=['bin/zaiste-cli'],
    ...
)

using the following script

#!/usr/bin/env python

import zaiste
print zaiste.cli()

and put the script inside bin directory

zaiste/
    zaiste/
        __init__.py
    setup.py
    bin/
        zaiste-cli

in order to run it as

$ zaiste-cli

Alternatively you can use console_scripts provided by setuptools so a Python function can be directly registered as command-line script. It will generate a standalone script shim which imports the module and calls the registered function.

setup(
    ...
    entry_points = {
        'console_scripts': ['zaiste-cli=zaiste.cli:main'],
    }
)

with cli.py defined as:

import zaiste

def main():
    print zaiste.cli()

and put directly inside a module

zaiste/
    zaiste/
        __init__.py
        cli.py
    setup.py

This method of adding command-line scripts is preferable as it is very easily testable:

from unittest import TestCase
from zaiste.cli import main

class TestConsole(TestCase):
    def test_basic(self):
        main()
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