Homework 2-2

Create a folder on your desktop called “HW2-2”. Download the starter program moby-starter.py and the text of Moby-Dick from the course website and save them in this folder. Right click on the Python program and select Edit with IDLE. When you write your functions, remember to write down what your functions does and what the arguments mean, by commenting your code. Remember that comments start with a #.

1. The starter program contains a function called printMD1000 that takes no arguments, and is supposed to print out the first one thousand characters in Moby-Dick. It needs to know where to find the MobyDick.txt on your computer, however. Modify the string 'C:\\WinData\\Desktop...' so that its value is the correct path to MobyDick.txt on your computer.
2. Look at the rest of the code for printMD1000 and make sure you understand why it should work. Then press F5 to run it. You should see another IDLE window come up. Then after the prompt type printMD1000() to call your function. Make sure it produces the correct answer. (You do not have to hand in anything for this part.)
3. Now, write another function called print1000 that takes one argument. Suppose in the folder “HW2-2”, I have bunch of text files: MobyDick.txt, Hamlet.txt, Bible.txt, etc. You want the argument to this function to tell the function which text file to print. For example, calling print1000('MobyDick.txt') should print the first 1000 characters of the file Z:\WinData\Desktop\HW2-2\MobyDick.txt, and calling print1000('Hamlet.txt') should print the first 1000 characters of the file Z:\WinData\Desktop\HW2-2\Hamlet.txt, assuming the file does exist. On your computer, the path to the HW2-2 directory will probably be different than Z:\WinData\Desktop\HW2-2; use the path that works on your computer instead. Hint: remember you can use the + operator to “glue” strings together.
4. Now you're going to test the function you just wrote. Provide one example of a call to print1000 (different from the ones we've provided) that works as expected.
5. Write a third function, printN, that takes two arguments. The first one indicates which file to print (same as the last function) and the second is a number indicating how many characters from the beginning to print. For example, calling printN('MobyDick.txt', 500) should print out the first five hundred characters in the file located at Z:\WinData\Desktop\HW2-2\MobyDick.txt.
6. Provide two examples of calls to printN that show that it works as expected. What are you looking for when you check that printN is correct?

When you're done, name your program YourName_MobyDick.py — for example, JadrianMiles_MobyDick.py.

Look at the following Python program (the numbers to the left of the line are line references and not part of the program):

numOfPC = 10
numOfMac = 4
inventory = [numOfPC, numOfMac]

def addOne(num):
  result = num + 1
  return result

addOne(numOfMac)
numOfPC = addOne(numOfPC)
inventory[1] = addOne(inventory[1])
    

1. Without actually running the program in Python, write down your prediction of the values of the variables numOfPC, numOfMac, and inventory after the program has executed lines 3, 9, 10, and 11. (Hint: when in doubt, review the way we reasoned about programs in class and follow it religiously). Write down these variables in a text file called YourName_HW2-2.txt — for example, JadrianMiles_HW2-2.txt.
2. Now open IDLE. Under the File menu in the top left corner, click on New Window (or simply press Ctrl+N on your keyboard). This should open up a new file as we saw in class. Type in the program.
3. By inserting some print statements, modify the program so that when you execute it, you can see what are the values of the variables numOfPC, numOfMac, and inventory after lines 3, 9, 10, and 11.
4. Save your program and name it YourName_HW2-2_Task2.py. (You need to hand in this program.) Then press F5 to run the program. Do the outputs match your prediction from the first question? If there is a difference, try to explain it. Write this solution in your text file.

In class, we gave a list of things that you should not do when writing a Python program. Remember the reason that we have these “taboos” is that we can reason about programs much more easily if we restrict our way of writing them. This task is meant to give you a taste about how whimsical programs can get if you defy these rules.

Danny, a naive Python programmer, wants to write a function that, given two variables, swaps their values. Here is what he wrote:

def swapBAD(a, b):
  '''Swap the values of two variables.'''
  temp = a
  a = b
  b = temp
  return
  
x = 10
y = 42
swapBAD(x, y)
print x, y
    

What do you think are the values of x and y at the end of the program? If you are not sure about your answer, test it by running the program. Explain in a few words why the swap function succeeds or fails. You should be able to do it by just following our in-class reasoning.

Write your solutions in the same text file as Task 1.

1. Write a function that determines if an integer a is in a list of integers myList. To do this, iterate through all elements in the list, and check if it is the same as the integer a. Once you see a match, return True. After the iteration, return False (why?). Be careful with the indentations!
2. (Extra Credit) Now write a function that determines if all of the integers in a list myList1 are in another list of integers myList2. To do this, iterate through all elements in myList1, and check if each element is in myList2 (hmm... sounds like a familiar task — maybe you can reuse the function you wrote for part 1). Again, just fill in the corresponding function skeletons in HW2-2.py.