Learning Python with a coding kata and TDD
This uses the Python nose testing framework.
To run:
nosetests mars-rover -v
Mars Rover Kata.
Taken from http://amirrajan.net/Blog/code-katas-mars-rover
– Develop an api that moves a rover around a grid.
– You are given the initial starting point (x,y) of a rover and the direction (N,S,E,W) it is facing.
– The rover receives a character array of commands.
– Implement commands that move the rover forward/backward (f,b).
– Implement commands that turn the rover left/right (l,r).
– The only commands you can give the rover are f,b,l, and r.
– Implement wrapping from one edge of the grid to another. (planets are spheres after all)
– Implement obstacle detection before each move to a new square. If a given sequence of commands encounters an obstacle, the rover moves up to the last possible point and reports the obstacle.
Here is an example:
– Let’s say that the rover is located at 0,0 facing North on a 100×100 grid.
– Given the command “ffrff” would put the rover at 2,2 facing East.
This was my first serious Python project. I've done katas and TDD before in other languages. So although I expected to learn some more about TDD and doing katas, the focus was on Python and its TDD framework.
Although I was originally a bit skeptical about Python, the documentation is pretty solid and the syntax is straightforward. It's not as fussy as Perl and Ruby. What I mean is, it avoids Perl's variable type sigils, '$', '%', etc., and it also avoids Ruby's similar global/local variable scoping sigils. It's more like JavaScript in terms of being loosely typed.
I did actually get used to the colon-indent structure.
Support for the common data structures is built into the language. I was quite impressed that even the set data structure is present. This is like Ruby and Perl, but very much unlike Java and C++ where libraries need to be explicitly imported to support data structures. This is admittedly only a first impression, due to the limited language scope required for this kata.
The unittest/nose framework even supports proper exception testing.
What I do miss is rspec-like test method structure which I've gotten used to in JavaScript (Jasmine, Mocha). There was some project that tried to address this, but I didn't check it out.
The 'with' keyword was used in the tests for exceptions. I just followed the example code, without fully understanding it.
I'm still noodling on the docs (TL;DR).
I think Python's approach to formatted strings - or templates - is unique. There are various ways to do it, but the one I chose is like this:
"template with substitution commands".format(arg1, arg2, ...)
This is actually kind of neat - I think it looks more like a transform pattern. It's very unlike the variable/expression interpolation of Ruby, PHP, bash, etc. I used it to add descriptive content to exception messages.
This Kata didn't provide an opportunity to dive into OOP with Python. The only thing I can mention, is the language relies on the explict 'self' variable in all method signatures. The need for 'self' is greatly eased by IDE support - IntelliJ automatically adds it for you.
I used IntelliJ in developing this kata. The Python plugin seems to provide all the usual language support - although for this kata I used only a bit of the features.
Python has a 'yield' keyword. Sounds similar to Ruby's, but don't know since I haven't tried Python's.
Python packaging and distribution, except for a little pip and easy_install.
Here's the tech debt I deliberately took on:
- Rover depends on Planet. Rover should depend on Position, which depends on Planet.
https://www.youtube.com/watch?v=Qw2vczm4m2c&feature=youtu.be
http://nose.readthedocs.io/en/latest/index.html
Note: nose is a superset of Python unittest
This gives three options for installing: easy_setup, pip, download.
On OS X El Capitan and later, SIP issues arise because the installers want to install in the pre-installed Python directory, /Library/Python/2.7/. SIP won't allow even sudo install there.
Well, sudo easy_install nose eventually worked.
The test runner is at /usr/local/bin/nosetests.
http://nose.readthedocs.io/en/latest/testing.html
Since one of my complaints was the desire for rspec-likee tests, check out Konira: https://github.com/alfredodeza/konira
Here are some issues I encountered in getting this to work.
After installing nose with pip, cannot find the executable in the path.
Executable should be in /usr/local/bin
Actually the problem is SIP on OS X El Capitan
http://apple.stackexchange.com/questions/209572/how-to-use-pip-after-the-os-x-el-capitan-upgrade
The Python plugin includes PyCharm
Preferences > Tools > Python Integrated Tools switch from unittests to nosetests