Fifth Class

Announcements

Feedback: G+ not a great place to turn in assignments. We'll start turning everything in via Github. Add draft= true to your posts if you don't want them to show up under your name.
Extra Credit Experience: Seeking commiters. Students who feel comfortable on Github and want commit access. These people will help me categorize issues, manage milestones, etc. We'll all eventually be core committers, but these are people who don't mind learning early. Email me.
Problem reports: You guys are going a great job in the community, reporting problems and helpping each other. Bonus points for reporting problems that tripped you up but you solved, along with the solution.
Post subdirectories: You can put your posts in a _posts subdirectory with your user name if you want. Helps keep things more organized. See _posts/elliott for an example.

Quesions?

Hands on

We're diving in. Don't worry about understanding in this first section- focus on getting things to work.

Hello Turtle

Fire up your Ubuntu instance. There are one or two of you who don't have Ubuntu installed. Use http://skulpt.org and make sure to contact me if you haven't already.
Open two terminal windows. You'll have to right click on the Terminal icon to get the second one. Put them so you can see them both. In one of them, type command sudo apt-get install python-tk and press enter to install the turtle module.
Type "python" in one of your terminals and hit enter. Look at the following code:

import turtle

edward = turtle.Turtle()

for color in ['red', 'blue', 'green', 'yellow']:
  edward.color(color)
  edward.forward(75)
  edward.left(90)

turtle.done()

Type it in your python console, line for line. You may run into errors. If you press up you can get to previous lines. The for loop will be trickiest: two spaces in front of those lines!

You should see a window pop up with an arrow (the Turtle) that makes a colored box. Awesome!

Interlude: nano

Typing into the console is fun, but there are faster ways to program.

There is a terminal text editor we'll be using called nano. Open it in your non-python window by typing "nano" and pressing enter. Nano is a great little program and is on almost every Linux computer. From now on, open a browser inside Ubuntu and you can copy and paste these programs into nano to get started. (you may even have configured the copy/paste between machines function)

The two nano commands you need to know for now are Ctrl-O to Output a file and Ctrl-X to Exit the program. You can also type nano file.txt to open file.txt. Nano will make this file for you if it doesn't exist. Most of our files will have a .py extension, which is idiomatic and turns on syntax highlighing (yay!).

Once you've created and saved a new file in your nano terminal, you should be able to run it in the other one. If you're still in the Python console, type quit() or Ctrl-C to get out of it. Then, type python edward.py (if your file's name is edward.py)

How's this Turtle stuff work?

Once your turtle is drawing a box, try to read what's going on in the code above for understanding. Then, read the code below that I've commented to help explain what's going on:

# Import the `turtle` module.
#
# Modules are bits of code someone else wrote for us.  They rock!
import turtle

# What's going on here?
#
# The `edward =` part is me defining a *name*.  This tells Python
# to go look at what's after the equals sign when I use the name.
#
# The name I've picked is 'edward'.  Names should be descriptive.
#
# After the equals sign is where it gets interesting.  We use the
# `turtle` name to reference the module we've imported.  The dot
# then tells python to look inside the module for something called
# `Turtle`.  The `()` just mean we aren't giving that `Turtle` thing
# any extra information. 
edward = turtle.Turtle()

# Now comes a `for` statement.
# 
# Python will take each of the things after the `in`, assign them
# to the `color_name` name, and then execute only the statements
# in the susequent block (the onews with two spaces in front of them)
for color_name in ['red', 'blue', 'green', 'yellow']:

  # Now what? `edward` seems to have things *inside* him.  These
  # are called "Methods" and they're something you have to read
  # the documentation (or see an example) to know about.
  # Each method lets us control the `edward` turtle in a different way.
  edward.color(color_name)
  edward.forward(75)
  edward.left(90)

# This line of code makes the window wait at the end.  Otherwise it
# closes.  Comment it out by adding a "#" in front of it to see.
turtle.done()

Check out the source code to turtle. Just skim it. It's well-documented code that you don't have to understand (or even read) to make turtles do fun things. That's a sign of a good library: easy and somewhat intuitive to use, with good documentation and instructions, and well formed, well commented code.

Many Paths to the Top of the Mountain

There are literally infinite ways to make the computer do this exact thing. Here's one:

import turtle

edward = turtle.Turtle()


# Old Code:
# for color in ['red', 'blue', 'green', 'yellow']:
#  edward.color(color)
#  edward.forward(75)
#  edward.left(90)

def draw_side(turtle_name, color, length, angle):
  turtle_name.color(color)
  turtle_name.forward(length)
  turtle_name.left(angle)

draw_side(edward, 'red', 75, 90)
draw_side(edward, 'blue', 75, 90)
draw_side(edward, 'green', 75, 90)
draw_side(edward, 'yellow', 75, 90)


turtle.done()

Read this code to try to see how it accomplishes the same thing.
Paste it into nano and add comments explaining what's going on.

Code & Creativity

There are many ways to make this turtle draw boxes, and many names to five him/her. In fact, you can even make the turtle draw other shapes.

This is the fun part of the class. Work alone or in groups to make an awesome turtle picture. Create multiple turtles, perhaps. Work on colors, or figure out how to get curved lines. Google and the Web are your friends, but keep track of any sources you use.

By the end of class (or the day), create a new post with your turtle code, any sources you used, and a screenshot of your turtle drawing. Bonus points for reflections, links to resources, or etc. Heck, you could even post a few :)

The SILShack class blog - Fall 2013