asimonia/python_koans

Python Koans - Learn Python through TDD

Python Koans

Python Koans is a port of Edgecase's "Ruby Koans" which can be found at http://rubykoans.com/.

Python Koans is an interactive tutorial for learning the Python programming language by making tests pass.

Most tests are fixed by filling the missing parts of assert functions. Eg:

self.assertEqual(__, 1+2)

which can be fixed by replacing the __ part with the appropriate code:

self.assertEqual(3, 1+2)

Occasionally you will encounter some failing tests that are already filled out. In these cases you will need to finish implementing some code to progress. For example, there is an exercise for writing some code that will tell you if a triangle is equilateral, isosceles or scalene.

As well as being a great way to learn some Python, it is also a good way to get a taste of Test Driven Development (TDD).

Downloading Python Koans

Python Koans is available through git on Github:

http://github.com/gregmalcolm/python_koans

It is also mirrored on bitbucket for Mercurial users:

http://bitbucket.org/gregmalcolm/python_koans

Either site will allow you to download the source as a zip/gz/bz2.

Installing Python Koans

Aside from downloading or checking out the latest version of Python Koans, you need to install the Python interpreter.

At this time of writing, there are two versions of the Python Koans:

• one for use with Python 2.7 (earlier versions are no longer supported)
• one for Python 3.1+

You should be able to work with newer Python versions, but older ones will likely give you problems.

You can download Python from here:

http://www.python.org/download

After installing Python make sure the folder containing the python executable is in the system path. In other words, you need to be able to run Python from a command console. With Python 2 it will be called python or python.exe depending on the operating system. For Python 3 it will either be python3 or for windows it will be python.exe.

If you have problems, this may help:

http://www.python.org/about/gettingstarted

Windows users may also want to update the line in the batch file run.bat to set the python path:

SET PYTHON_PATH=C:\Python27

Getting Started

Jake Hebbert has created a couple of screencasts available here:

http://www.youtube.com/watch?v=e2WXgXEjbHY&list=PL5Up_u-XkWgNcunP_UrTJG_3EXgbK2BQJ&index=1

Or if you prefer to read:

From a *nix terminal or windows command prompt go to the python koans\python_VERSION folder and run:

python contemplate_koans.py

or:

python3 contemplate_koans.py

In my case I'm using Python 3 with windows, so I fire up my command shell (cmd.exe) and run this:

Apparently a test failed:

AssertionError: False is not True

It also tells me exactly where the problem in, its an assert on line 12 of .\koans\about_asserts.py. This one is easy, just change False to True to make the test pass.

Sooner or later you will likely encounter tests where you are not sure what the expected value should be. For example:

class Dog:
    pass

def test_objects_are_objects(self):
    fido = self.Dog()
    self.assertEqual(__, isinstance(fido, object))

This is where the Python Command Line can come in handy. In this case I can fire up the command line, recreate the scenario and run queries:

Sniffer Support

Sniffer allows you to run the tests continuously. If you modify any files files in the koans directory, it will rerun the tests.

To set this up, you need to install sniffer:

$ pip install sniffer

You should also run one of these libraries depending on your system. This will automatically trigger sniffer when a file changes, otherwise sniffer will have to poll to see if the files have changed.

On Linux:

$ pip install pyinotify

On Windows:

$ pip install pywin32

On Mac OS X:

$ pip install MacFSEvents

Once it is set up, you just run:

$ sniffer

Just modify one of the koans files and you'll see that the tests are triggered automatically. Sniffer is controlled by scent.py

Getting the Most From the Koans

Quoting the Ruby Koans instructions:

"In test-driven development the mantra has always been, red, green,
refactor. Write a failing test and run it (red), make the test pass
(green), then refactor it (that is look at the code and see if you
can make it any better). In this case you will need to run the koan
and see it fail (red), make the test pass (green), then take a
moment and reflect upon the test to see what it is teaching you
and improve the code to better communicate its intent (refactor)."

Content

The Python Koans is a made up of about 2/3 Ruby Koans ported material and 1/3 Python specific tests. The content ported from Ruby Koans includes all the assignment projects.

Content for Python 3 is a little different to the Python 2 flavor due to big changes between the two different versions of the language. For example, in the Python 2 variant the differences between old and new style classes are covered. This loses relevance in in the Python 3 version, but there are some extra tests covering new functionality.

Finding More Koan Projects

There are number of other great Koan projects out there for various languages and frameworks. Most of them can be found in github. Also there is a little koans activity on bitbucket.

• Github koan projects:

  https://github.com/search?q=koans&ref=cmdform

• Bitbucket koan projects:

  https://bitbucket.org/repo/all?name=koans

Acknowledgments

Thanks go to Jim Weirich and Joe O'Brien for the original Ruby Koans that the Python Koans is based on! Also the Ruby Koans in turn borrows from Metakoans so thanks also go to Ara Howard for that!

Also thanks to everyone who has contributed to Python Koans! I got a great headstart by taking over a code base initiated by the combined Mikes of FPIP. So here's a little plug for their very cool Python podcast:

http://frompythonimportpodcast.com/