E D - Environmental Dependencies in Python
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Overview of dependency management and virtual environments in python. This a very high level primer with links for further reading.
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E D - Environmental Dependencies in Python
- 1. E D ENVIRONMENTAL DEPENDENCIES IN PYTHON
- 2. Building Highly Complex Systems Many pieces acting as one Image by Alan_D from Crawley, United Kingdom - Nissan GTR Cutaway, CC BY 2.0, https://commons.wikimedia.org/w/index.php?curid=18072247
- 3. Building Open Source Business Systems Using what you can find to build what you need Image byy Mick from England (Go Kart Buggy) [CC BY 2.0 (http://creativecommons.org/licenses/by/2.0)], via Wikimedia Commons
- 4. Python Tools Core tools for dependency management in Python Image by Alexander Baxevanis (Flickr: Cooper's tools) [CC BY 2.0 (http://creativecommons.org/licenses/by/2.0)], via Wikimedia Commons
- 5. One Language Multiple Tools Dependency Management Easy Install – deprecated Distutils – deprecated Setuptools – project dependencies PIP – environment dependencies Environment Management venv – Python 3.3+ Virtualenv – Virtual environments Virtualenvwrapper – Enhancements for Virtualenv
- 6. setuptools Project dependency management Image by ParentingPatch (Own work) [CC BY-SA 3.0 (http://creativecommons.org/licenses/by-sa/3.0)], via Wikimedia Commons
- 7. Setuptools – Project Dependency Tool Defines package information: name, version, authors, etc. Defines package and test dependency requirements for project source Should define as wide a range as possible for dependency versions Builds distributions Publishes distributions to PyPI Defines scripts to install as binaries Provides runtime support for C modules Can be used for test bootstrapping
- 9. Setuptools setup.py … setup(name='launchkey-python', version='1.3.0', … install_requires= [ 'pycrypto >= 2.6.1', 'pycrypto < 3.0.0', 'requests >= 2.5.1', 'requests < 3.0.0', 'six >= 1.10.0', 'six < 2.0.0', ], tests_require=[ 'Mocker==1.1.1', 'mock==1.3.0' ], )
- 10. pip Environment dependency management Image © Dietmar Rabich, rabich.de - Own work, CC BY-SA 4.0, https://commons.wikimedia.org/w/index.php?curid=34239265
- 11. PIP Requirements File Overview Contains information for repeatable installs Can include command line options Can use a constraints file for multi-project dependency version overrides. Helpful for using patched forks Can be built with the freeze command Example --index-url=https://my-pypi.example.com pycrypto==2.6.1 requests==2.10.0 six==1.10.0
- 12. PIP Freeze $ pip freeze > requirements.txt cat requirements.txt launchkey-python==1.3.0 pycrypto==2.6.1 requests==2.10.0 six==1.10.0 Use the PIP freeze command to generate a requirements file based on the currently installed versions.
- 13. Virtual Environments Different parts for different projects Image by EncMstr (Own work) [GFDL (http://www.gnu.org/copyleft/fdl.html) or CC BY-SA 4.0-3.0-2.5-2.0-1.0 (http://creativecommons.org/licenses/by-sa/4.0-3.0-2.5-2.0-1.0)], via Wikimedia Commons
- 14. Virtualenv Can be installed via PIP Allows you to switch between “virtual” environments Virtual environments are full copies with symbolically linked, or optionally copied, python binaries including pip. Private set of environment variables Private set of installed packages Can be told which Python executable to use Environments can be easily activated and deactivated Deleting created directory remove virtual environments
- 15. Usage $ which python /usr/local/bin/python $ virtualenv --prompt "(sdk) ” .venv … Installing setuptools, pip, wheel...done. $ source .venv/bin/activate (sdk) $ which python /.venv/bin/python (sdk) $ deactivate $ which python /usr/local/bin/python Simple example for creating, activating, and deactivating virtual environments with Virtualenv
- 16. Virtualenvwrapper Can be installed via PIP Adds additional functionality to Virtualenv Uses named rather than location based environments Places reusable environments in user directory Auto-complete for enabling and removing environments Defaults prompt prefix to environment name If directory is same name as project. Enable with directory location
- 17. Usage $ which python /usr/local/bin/python $ mkvirtualenv example … Installing setuptools, pip, wheel...done. (example) $ which python ~/.virtualenvs/example/bin/python (sdk) $ deactivate $ which python /usr/local/bin/python Simple example for creating, activating, and deactivating virtual environments
- 18. Pyenv Manage any number of Python executable versions Great for open source projects that need to run on multiple versions Has Virtualenv support via an add-on to support mixing Python executable versions and virtual environments in a manner similar to rbenv. On Mac, make sure XCode and Command Line Developer Tools are up to date.
- 19. Usage $ which python3 $ pyenv install 3.5.2 Downloading Python-3.5.2.tgz... -> https://www.python.org/ftp/python/3.5.2/Python- 3.5.2.tgz Installing Python-3.5.2... Installed Python-3.5.2 to ~/.pyenv/versions/3.5.2 $ pyenv global 3.5.2 $ python3 --version Python 3.5.2 Simple example for installing and using a Python version
- 20. Further Reading Packaging: https://packaging.python.org/ Python Versioning: https://www.python.org/dev/peps/pep-0440/ Setuptools: https://setuptools.readthedocs.io/en/latest/ PIP: https://pip.pypa.io/en/stable/ PIP Version Resolving: https://github.com/pypa/pip/issues/988 Virtualenv: https://virtualenv.pypa.io/en/stable/ Virtualenvwrapper: http://virtualenvwrapper.readthedocs.io/en/latest/index.html Pyenv: https://github.com/yyuu/pyenv
Editor's Notes
- Modern applications are much like this Nissan GTR. Users of your application see a pleasantly crafter user interface. The myriad of dependent systems are hidden away. These systems interact via well defined interfaces and can be swapped out for a newer version of the part as it comes along and the user wouldn’t know the difference. In many vehicles, entire subsystems are built by entirely different companies and available either as stock or aftermarket upgrades. Your application is no different.
- Go karts are very similar to a GT-R. They are four wheeled rear wheel drive automobiles. They don’t have as many features as GT-R but they both do basically the same thing: go, stop, and turn. The biggest difference between them is the amount of design and engineering time put into them. For the car alone, it takes two to four years of design. Remember that that includes mostly ready made parts. The amount of time and engineering it takes for those is astronomical as well. They make up for the time in those parts by using them on multiple products. What most of us build are much less complex and we don’t build most of the pieces. We start with a framework and cobble together bits and pieces to build a functional application as quickly and efficiently as possible.
- Environments refer to python interpreter and a set of installed modules and extensions. Much like a factory, without environment tools, you would need reset the line by uninstalling current modules and extensions and installing the ones you need. By default, each Python executable has only one environment. You can make pseudo-environments by altering paths and setting environment variables but there is a better way. You can get project specific virtual environments with a few simple tools.