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README.md

Lesson 06: Development Environment and Tooling

Here are some key notes taken from this lesson which may help with the exercises.

Package Management

The Problem: Python has a "batteries included" philosophy - it has a comprehensive standard library, but by default, using other packages leaves something to be desired:

  • Python doesn't have a classpath, and unless you are root, you can’t install new packages for the whole system.
  • How do you share a script with someone else when you don't know what packages are installed on their system?
  • Sometimes you have to use ProjectA, which relies on a package that requires awesome-packagev.1.1, but you're writing ProjectB and want to use some features that are new in awesome-packagev.2.0?
  • The best-in-class package manager isn't in the Python standard library.

The Solution: virtualenv

The virtualenv package creates virtual environments, i.e. isolated spaces containing their own Python instances. It provides a utility script that manipulates your environment to activate your environment of choice.

The -p flag indicates which Python executable to use as the base for the virtual environment:

$ virtualenv NEWENV -p /usr/local/bin/python
$ source NEWENV/bin/activate
$ deactivate

A virtual environment has the package manager pip pre-ihstalled, which can be hooked into the internal mirror of the Python Package Index (PyPi) by exporting the correct address to the PIP_INDEX_URL environment variable.

$ source NEWENV/bin/activate
$ pip install requests

import requests
import sys

print(requests.__version__)
print(sys.path)

Now we have a place to install custom code and a way to share it!

  • Develop code inside ~/NEWENV/lib/python2.7/site-packages
  • Capture installed packages with pip freeze >> requirements.txt and install them to a new virtualenv with pip install requirements.txt

The Ultimate Package

IPython is an alternative interactive shell for Python with lots of cool features, among which are:

  • tab completion,
  • color output, -rich history recall,
  • better help interface,
  • 'magic' commands,
  • a web-based notebook interface with easy-to-share files, and
  • distributed computing (don't ask about this)
$ pip install ipython
$ ipython

# To use the web interface, you have to install supplemental packages:
$ pip install pyzmq tornado jinja2 pygments
$ ipython notebook --no-mathjax

# Just two more packages are required to get awesome inline graphics
$ pip install numpy
$ pip install matplotlib