Day 12 – Th, Feb 14th, 2013¶
Rough schedule for today, summary:
- review classes in Python, below
- read about refactoring, below
- read and work through HTML example, below (optional)
- read hw3 carefully and ask questions!
- work on examples and HW; ask questions; run about, scream and shout
- minute cards
Classes and objects in Python¶
Classes can be defined like so:
class MyClass(object):
def __init__(self, ...):
...
def method1(self, ...):
...
and then instantiated like so:
x = MyClass(...) # <-- __init__ arguments; no self needed.
Instantiating a class creates an empty object and then runs __init__ on it. You call methods on objects like so:
x.method1(...) # no self needed; it's passed in explicitly.
Note that the method1 call, above, is identical to:
MyClass.method1(x, ...)
where ‘x’ must be an object of type MyClass.
Objects are, in essence, namespaces with behavior: that is, they contain other objects (self.x, self.y, self.z, etc.) and behavior on them, in the form of methods. See cse491-numberz/series_iter/series.py for a really simple example of this.
See tutorialspoint for more info, or use the Google.
Refactoring¶
Refactoring is a really valuable buzzword to know.
Refactoring is the art of making code nicer (more modular, better organized, etc.) without changing functionality. Most students think it’s a waste of time because they only work on one homework at a time; they’re wrong. If you consistently refactor your code to be cleaner, more modular, and better tested, then over time your underlying project will get much easier to modify and extend without fear.
Automated tests are a really valuable component of this.
In fact, one of the most important uses of tests is to support refactoring – when refactoring, you should only add tests to test newly factored out bits of functionality, and never change existing tests or remove them (unless you remove a function, but then you should refactor the test so it still tests the same underlying functionality).
For an example of refactoring, see: Refactoring Example
Basis HTML output and linking - discussion and exercise¶
The 10-second introduction to HTML: HTML, which is how most Web pages are formatted, consists of display instructions inside of angle brackets, e.g.
<b>Make this text bold</b>, and leave this text not bold.
If you put that in a file named ‘bold.html’ and opened it in a Web browser, you would see the first bit bold and the second bit not bold. The tags <b> and </b> would not be visible. If you forget to “close” the <b> tag with </b>, then all of the text would be bold.
Let’s try it out.
Go grab github.com/ctb/cse491-linkz, clone it, and run ‘python make-html.py’. Now open html/index.html in a Web browser (see below for instructions on working remotely on the CSE cluster) and click around.
Now, go into make-html.py and read through it, and then:
- Create a new file ‘link.html’ that contains ‘Hello, world’ in bold.
- At the bottom of table.html, add a link to ../index.html to go back “up” in the site hierarchy. Note the connection between the directory structure and URLs.
- Fix the output of ‘catastrophe.html’ by closing the h3 tags correctly, and then link catastrophe.html into the bottom of index.html as ‘check out the catastrophe!’
Could people post HTML tutorials that they found useful, please? Either in the comments on this page, or to the mailing list?
Posting Web pages on your CSE account¶
If you have a CSE account and are working remotely on the CSE machines, something like the following should work to post HTML pages at www.cse.msu.edu/~username. (Also read: http://www.cse.msu.edu/facility/howto/mywebpage/)
python make-html.py
mkdir ~/web
chmod a+rx ~/web
rm -fr ~/web/cse491-linkz
cp -r html ~/web/cse491-linkz
chmod -R a+rx ~/web/cse491-linkz
You can then update this with your HTML diretory by doing:
rm -fr ~/web/cse491-linkz
cp -r html ~/web/cse491-linkz
chmod -R a+rx ~/web/cse491-linkz
Homework 3 - readme¶
Read through Homework #3; note that there are several branches to merge for various bits of the homework. You can do this all at once (recommended) or do it as you implement the functionality.
Especially check out the test format I used on the hw3-recipe-tests branch in test_recipes.py, and read about test fixtures to understand the setUp and tearDown functionality in hw3-recipe-tests.
Minute Cards¶
In the last 5 minutes of class, please fill out this minute card survey.