Part A.1.A: Loops

Suggested Reading: Sections 7.3 and 7.4

First, we will introduce loops. This allows our program to repeat tasks for a set number of times or until some criteria is met. Open the file loops.py.

Programming Exercises

1. First go into the Your_script directory. Here you will find a blank python script called your_script.py. This will be the file that should contain your code for lab 1 part 1.
   
   
2. Without using a for or while loop create a function called count_to_n that takes one variable, n. The variable n can be equal to 1, 2, or 3. Using a conditional statement, get your code to print all integers starting from 1 up to n. Each integer should be printed on it's own line. Check to make sure your function works properly for the integers 1, 2, and 3.
   
   
3. Next, create two functions called count_to_n_for and count_to_n_while that takes one variable, n. This variable can be equal to any integer. Using a for and while loop respectively, get these functions to print all integers starting from 1 up to n. Each integer should be printed on it's own line. Check to make sure both functions work properly for integers 2 and 10.
   
   
4. Create a function that computes the sum of all numbers divisible by 2 and 7 that are less than 200 using a loop and a conditional statement. Print the sum you compute. i
   
   Note: This question maybe interpreted as summing all numbers divisible by 14 or summing numbers divisible by 2 and numbers divisible by 7. Either interpretation will be correct.

Part A.1.B: List

Suggested Reading: 10.1 through 10.4

Next, we will learn more about lists, a variable type that holds a list of other variables. We will learn how to create, access, and change them. Open the file lists.py.

Programming Exercise

1. Go into the Your_script directory, open your_script.py, and at the bottom of this script print "Part 1B".
   
   
2. Create a variable called intlist3 that lists all of the integers containing 0 up to 3 without using a loop.
   
   
3. Create a variable called intlist9 that is a list containing the integers 0 up to 9 using a for loop.
   
   
4. Create a variable called two_n that is a list containing 2ⁿ from n = 0 to n=9. Print 2⁷ by indexing two_n.
   
   
5. Create a for loop that iterates over the list you just created, two_n. In this for loop indicate how many elements of this list are divisible by 8.
   
   
6. Create a 2x2 matrix called matrix where the first row is the list, [3,4], and the second row is the list [5,6]. Then use indexing to print the second row of this matrix and the first entry of the first row.
   
   
7. Go back one directory via command line to prepare for part 1C.

Part A.1.C: More Numpy Tools

Next, we will learn some more of the tools Numpy has to offer! Open then run the file numpy_ex.py.

Programming Exercise

1. Go into the Your_script directory, open your_script.py, and at the bottom of this script print "Part 1C".
   
   
2. Create the variable called two_n_1 and two_n_2 which will both re-create two_n from Part 1B, but this time utilize numpy in the following ways:
   
   
   1. For two_n_1 use numpy to create an array of all zeros with length 10. Then assign the correct value using a for loop.
   2. For two_n_2 initialize an empty numpy array, then append each new value using a for loop.
   
   
3. Determine the average of the values in the array two_n.
   
   
4. Next create a variable called three_n that is a array containing 3ⁿ from n = 0 to n=9. Print the array, three_n. Then compute and print an array containing 3ⁿ - 2ⁿ from n = 0 to n=9 without using an additional loop.
   
   
5. Create four variables called array_1, array_2, list_1, and list_2. If it has array in the name, it should be a numpy array. If it has list in the name, it should be a python list. The array_1/list_1 is [1.,2.] and the array_2/list_2 is [3.,4.]. Use the addition arithmetic operator and print the sum of list_1 and list_2. Use the addition arithmetic operator and print the sum of array_1 and array_2. Print a string explaining how list and numpy array addition arithmetic is different.
   
   
6. Using numpy, compute the magnitude of the vector [5.3,6.2,9.5]. (Hint: there is a numpy function that will do this for you called norm!)
   
   
7. Then create a function which takes any numpy array and returns its cooresponding unit vector or normalized vector. You can calculate the unit vector by dividing each component in a vector by the magnitude of that vector. Test this function using the vector used in the previous question.

Part A.1.D: Scope and reading and writing files

Programming Exercise

1. The scope of a variable is a CS term used to define where variables are valid in your script. Take a look at and run the script scope.py. Then, edit this script so that it no longer has errors and according to the instructions in the script.
   
   
2. Take a look at and run the script called write_files.py. Then, Take a look at and run the script called read_files.py
   
   
3. Go into the Your_scripts directory and at the bottom of this script print "Part 1D".
   
   
4. You can generate the Fibonacci sequence by starting with the numbers 1 and 1. Then, add the last two numbers in the sequence to get the following number in the series. Here are the first few numbers in the series:
   
   1, 1, 2, 3, 5, 8, 13, 21 ....
   
   Determine the Fibonacci sequence up to the number 610 and write this sequence to a file called fibonacci.txt .
   
   
5. Then, edit your_script.py so that it reads back in the file fibonacci.txt using readlines. Use a while loop to print each number in the Fibonacci sequence up to 610 (or each line in the fibonacci.txt file). Recall that you can determine the length of an array using len function.
   
   
6. You have now made all the required edits to your_script.py. Record the path to your_script.py to a word document like Google Docs or Microsoft Word. Then, move on to part 1E.

Part A.1.D: Debugging

As you may already realize, debugging is a critical skill in programming! Below we will discuss common mistakes that are made in Python, alongside common strategies to identify and fix them.

In general, there are two kinds of errors. There are errors that will stop your script from running, and there are errors that will let your code finish running but won't behave like you thought it would. Just because your code runs, it isn't necessarily right.

Common Python errors include: whitespace errors, missing colons, missing quotation marks, missing parentheses or brackets, and not defining variables in the correct place (ie. scope errors).

Here are common strategies for fixing simple scripts:

Reading the error message: The first step to fixing an error is identifying what the error is. If your code prints an error message, read it. It will tell you what kind of error there is and what line it's in. Here is a list of error types Python could throw your way.

Printing variables: This is a goto for figuring out where your code is not doing what you thought it was. Printing values before and after function calls, for example, can help determine if the function is behaving as expected.

Tracing your code: Tracing your code by hand is a skill. Sit down with pen and paper, and walk through your code line by line as if you were the computer, writing down variables and changing their values, looping through loops, going back to functions -- everything. Doing this meticulously will help you find logical errors you've made. If your tracing doesn't match up, use print statements to find exactly where your understanding diverges from the code.

Your last task of this assignment is to debug two python scripts, debugging.py and debugging2.py. Remember that your script may run without errors, but there may still be bugs in your script. After debugging the scripts, add the path to the scripts on the same word document that contained the your_script.py path.

Here is some useful information for the script debugging2.py. You can generate the Fibonacci sequence by starting with the numbers 1 and 1. Then, add the last two numbers in the sequence to get the following number in the series. Here are the first few numbers in the series:

1, 1, 2, 3, 5, 8, 13, 21 ....

This script contains 4 functions which all produce the Fibonacci sequence.