Appendix 1: Optional Refresher on the Unix Environment

A1.1) A Quick Unix Overview

In Jupyter, many of the same Unix commands we use to navigate in the regular terminal can be used. (However, this is not true when we write standalone code outside Jupyter.) As a quick refresher, try each of the following:

We're in a new folder now, so issue commands in the next two cells to look at the folder content and list your current path:

Now test out a few more things. In the blank cells below, try the following and discuss in your group what each does:

What does the asterisk symbol * do?

Answer: Is a placeholder (wildcard) for some text in a file/folder name.

Now, return to where you started, by moving up a directory:

(one directory up from where you are is denoted with .., while the current directory is denoted with .)

A1.2) A few more helpful commands

mkdir to make a new directory:

mkdir new_project_name

cp to copy a file:

cp existingfile newfilename
or
cp existingfile newlocation

mv to move or rename a file:

mv old_filename_oldlocation old_filename_newlocation
or
mv old_filename_oldlocation new_filename_oldlocation

rm to PERMANENTLY delete (remove) a file... (use with caution):

rm file_I_will_never_see_again

In the six cells below:

(1) Make a new directory, called temporary

(2) Go into that new directory

(3) Move the file test_file.txt from the original directory above (../test_file.txt) into your current location using the .

(4) Create a copy of test_file.txt with a new, different filename of your choice.

(5) Delete the original test_file.txt

(6) Go back up into the original location where this notebook is located.

If all went according to plan, the following command should show three directories, a zip file, a .png file, this notebook, and the Lab6 notebook:

And the following command should show the contents of the temporary folder, so only your new text file (a copy of test_file.txt, which is now gone forever) within it:

Appendix 2: Optional Refresher on Conditional Statements and Iteration

A2.1) Conditional Statements

The use of tests or conditions to evaluate variables, values, etc., is a fundamental programming tool. Try executing each of the cells below:

You see that conditions are either True or False (with no quotes!) These are the only possible Boolean values (named after 19th century mathematician George Boole). In Python, the name Boolean is shortened to the type bool. It is the type of the results of true-false conditions or tests.

Now try executing the following two cells at least twice over, with inputs 50 and then 80.

The four lines in the previous cell are an if-else statement. There are two indented blocks: One comes right after the if heading in line 1 and is executed when the condition in the if heading is true. This is followed by an else: in line 3, followed by another indented block that is only execued when the original condition is false. In an if-else statement, exactly one of the two possible indented blocks is executed.

A2.2) Iteration

Another important component in our arsenal of programming tools is iteration. Iteration means performing an operation repeatedly. We can execute a very simple example at the command line. Let's make a list of objects as follows:

This is an example of a for loop. The way a for loop works is a follows. We start with a list of objects -- in this example a list of strings, but it could be anything -- and then we say for variable in list:, followed by a block of code. The code inside the block will be executed once for every item in the list, and when it is executed the variable will be set equal to the appropriate list item. In this example, the list names had four objects in it, each a string. Thus the print statement inside the loop was executed four times. The first time it was executed, the variable n was set equal to Henrietta. The second time n was set equal to Annie, then Jocelyn, then Vera.

One of the most common types of loop is where you want to loop over numbers: 0, 1, 2, 3, .... To handle loops of this sort, python provides a simple command to construct a list of numbers to iterate over, called range. The command range(n) produces a list of numbers from 0 to n-1. For example:

There are also other ways of iterating, which may be more convenient depending on what you're trying to do. A very common one is the while loop, which does exactly what it sounds like it should: it loops until some condition is met. For example: