Due: Tuesday, February 7, 2017, 11:59 pm
The purpose of this lab time is to give you an introduction to the basic tools we will be using this semester. These tools include a terminal, a text editor, and the Python interpreter.
Labs and projects are tightly coupled. Each project is initiated with a set of lab exercises. In the projects, you will write code that expands on the code written in lab. For each project, you will be writing Python code and running it. The programs typically create images. You will be posting some of these images, along with a description of the project, on a Wiki page. You will then turn in your code by putting it in a special directory on one of the campus computer servers. Today's lab will allow you to practice each of these tasks.
Open up the Terminal application, which is a text-based method of using your computer.
A terminal is simply a text-based interface to the computer. In a terminal, you can type commands, manipulate files, execute programs, and open documents. Anything you can do in the Finder, you can do in a terminal (the reverse is not true).
When working in a terminal, the current directory is called your working directory. A terminal will usually start in the home directory of your account.
In a terminal we often need to specify a file or directory on the hard drive. The complete description of where a directory or file on a computer is located is called its path.
Directories in a path are separated by a forward slash /. The topmost directory on the filesystem is indicated by a single slash. The directory tree for your computer is all relative to the top level directory. In other words, starting with a /, you can type the complete path to any file on your computer. For example, the following is the path to my home directory.
Most of the time, however, you will be specifying paths relative to your current directory. Any path that starts without a slash is relative to your current working directory. Note that paths are case-sensitive, so be sure to use proper capitalization.
You will use paths, and filenames to change directories, list the contents of directories, and run Python programs.
Some important terminal commands are the following. We'll walk through how to use them together in lab.
ls- with no argument, ls lists the files in the current directory. If you put a path after the ls command, it will list the contents of the specified path.
cd <directory>- change directory. If you use t he command with no arguments, it changes the directory back to your top-level home directory. The current directory is specified as
.and the parent directory of the current working directory is specified using
|cd||Set the current directory to your home directory|
|cd ~||Set the current directory to your home directory. (The ~ character is shorthand for your home directory.)|
|cd ..||Move up to the parent directory of the current directory|
|cd blah||Move into the sub-directory blah|
|cd -||Move to your last working directory|
mv <from> <to>- move a file, including just renaming it in the current directory. The mv command will remove the file in the old location after copying it to the new location.
cp <from> <to>- copy a file to a new location or name
rm <filename>- remove the file (will not remove a directory). Note that this is not the same as dragging a file to the trash. It cannot be undone. Once the filed as been removed, it is gone for good.
rm -r <directory>- remove the directory and all the files and subdirectories in it
Some useful terminal properties are the following.
Wildcard characters: the star character
* is a
wildcard character. If you want to see all the files in a directory
that start with A, you can type:
A possibly bad thing to do is to type
Tab completion: when you have typed part of the name of a file or program, pressing the tab key will complete the filename as far as possible while the choice is unique. For example, if you have only one file that starts with the letter b, then typing b and then the tab key will complete the filename.
If you have two or more files that start with b, tab completion will beep at you. If you press tab again, then the terminal will show you the options (all the files that start with b).
Some useful (but not as common) terminal commands are the following.
pwd- tells you the complete pathname of the current directory
less <filename>- scroll through a file
cat <filename>- send the file to standard output
echo "a string"- write the text within the string to standard output
touch <filename>- touch either updates the modification date on a file or creates an empty file if the named file does not exist. This can be useful in various situations, like when you are learning to create, rename, and delete files using a terminal.
A fileserver is a central file system you can access from any computer. It's like having a virtual USB key you can plug into a computer to store your files. Colby maintains two different fileservers we use in this course. One (the Personal server) is for you to store the code you are working on. The other (Courses) is for you to turn in code. We will give instructions regarding the Courses directory in the project instructions. For now, let's focus on where you should keep code that is work in progress.
There are two ways to mount the file server.
Option 1: Load the root server directory and navigate to your directory.
You can mount the Colby fileserver root directory by going to the Finder and typing cmd-K, or selecting 'Connect To Server...' from the Go menu. It will bring up a dialog box, into which you want to enter the following.
and then click on the appropriate directories until you find your personal directory.
Option 2: Mount your directory directly.
You can mount your personal directory explicitly using the the following path in the 'Connect To Server...' dialog.
This system is backed up regularly, and you can access it from any computer on the Colby network. We strongly suggest you store all of your work for this course into your personal directory. You can, in fact, work directly from your personal directory. Let's practice doing that for the first project.
In the terminal, navigate to it. Type cd followed by the path to the directory. E.g. for Bruce, it may look like this:
Or, use a shortcut. If you type cd in the terminal, then drag the icon for your directory onto the terminal, then the path to it will automatically be pasted.
Text editors are the workhorse programs for writing code. You don't want fancy fonts or WYSIWYG layouts, you just want to see lines of text, preferably with syntax highlighting, which means that special words in a language are highlighted to make it easier to read the code. There are many editors to choose from.
In lab, I will be using TextWrangler. It is a free text editor for the Mac and it has all the features I need for writing programs. If you would like to install it on your personal computer, go to the TextWrangler web site and follow their instructions.
Put in the line:
print 'You are smart'
Now, you can instruct Python to run the program. In the terminal type
Congratulations, you just ran your first Python program. (Python humor)
Note that it works only if the current working directory is the one that contains the file smart.py. So, one thing you need to do when working on a project is to ensure that your Terminal is in the right directory. Think of it as making sure TextWrangler and Terminal agree about where the programs are. Note that, in general, you run Python programs by typing
For your information
Here are some other text editors you should know about:
If you open emacs, the opening screen tells you how to access a tutorial. The most important thing to know is how to save and get out. To save, hold the control key down and type x then s (C-x C-s). It will ask you for a filename (and give you a default if you opened a file) and then save it. To exit, hold down the control key and type x then c (C-x C-c).
Python is a simple yet powerful interpreted language for making computers do stuff. Many people have written modules for Python that do some sophisticated things. One of those modules is called turtle and implements turtle graphics (e.g. forward, left, right, pen down, and pen up).
We can make the turtle move forwards, backwards, turn left, turn right, and pick up or put down the pen using the following commands.
forward(x)- move forward x pixels
backward(x)- move backward x pixels
left(a)- turn left a degrees
right(a)- turn right a degrees
up()- pick up the pen (don't draw when the turtle moves)
down()- put the pen down (draw when the turtle moves)
More complete documentation is available on the Python documentation site. Let's write our first turtle program.
from turtle import *
That will import all of the turtle commands (i.e. it will give you the ability to direct the turtle to draw for you.)
raw_input('Press Enter to continue')
That will keep the turtle window open until you press return in the terminal. When you are finished, save a copy of your Python file to your directory on the Personal server.
forward(100) right(90) forward(100) right(90) forward(100) right(90) forward(100) right(90)
Colby Wiki - a Wiki is a convenient way to put content up on the web quickly and easily. We'll watch a video on how to create your personal space and then go through the process of creating a new page in your space.
Log in to the wiki, but wait until Ying says "Your turn" before clicking on the "Create your personal space" link. The system can't handle more than one space-creation at a time.
For each project, you will create a new page in your wiki space. You can edit any page in your space by going to the Edit tab. There you will find one or two options for editing your page. The Rich-text option (available when using FireFox browser) lets you do the normal select and point and click type formatting. The wiki markup lets you use the wiki markup language to make your page.
For your information
If you ever need to remove a page, go to that page and select "Remove" from the "Tools" menu in the upper right.
Remember to save your wiki page before navigating away from it. The wiki won't detect it and remind you.
When you are done with the lab exercises, you may start on the rest of Project 1.
© 2017 Ying Li. Page last modified: .