CS8 Final Exam E03, 09M, Phill Conrad, UC Santa Barbara 09/10/2009

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1 CS8 Final Exam E03, 09M, Phill Conrad, UC Santa Barbara 09/10/2009 Name: Umail umail.ucsb.edu Please write your name only on this page. That allows me to grade your exams without knowing whose exam I am grading. This exam is closed book, closed notes, closed mouth, cell phone off, except for: You are permitted one sheet of paper (max size 8.5x11") on which to write notes These sheets will be collected with the exam, and might not be returned Please write your name on your notes sheet There are 100 points worth of questions on the exam, and you have 2.5 hours (150 minutes) to complete the exam. I don't expect you to need all of that time, though you are welcome to use it if you do. A hint for allocating your time on your first pass through the exam: if a question is worth 10 points, spend no more than 10 minutes on it if a question is worth 20 points, spend no more than 20 minutes on it if a question is worth 40 points, spend no more than 40 minutes on it etc. If you do that, you'll complete your exam in 100 minutes (1 hour, 40 minutes). You'll then have another 50 minutes to: revisit any questions where you need more time check your work.

2 1. (20 pts) Write a function called countints. The function should take one parameter called thelist. If the value passed in for thelist is not a list, the function should return the string "error". Otherwise, the function should examine each item on the list, and count the number of items that are integers. Note that for this problem it is not an error for the list to contain things that are not integers it is only an error if the value of the parameter is not a list. See the test cases below for more clarification of how the function should operate. For purposes of this this exam, is is not required to put a "docstring" or header comment on your function. (Hints/Reminders: the Python type for integer is int, and the Python built-in function type returns the type of its argument.). check_expect("countints test1",countints([]),0) check_expect("countints test2",countints([1,2,3]),3) check_expect("countints test3",countints(['a','b','c']),0) check_expect("countints test4",countints([1,'a',2,3]),3) check_expect("countints test5",countints(['a',2,3,4,5]),4) check_expect("countints test6",countints([2,3,4,5,'1']),4) check_expect("countints test7",countints(1),"error") You do not need to write the check_expect function, or recopy the test cases.

3 2. (18 pts) On lab07, you were asked to replace a stub with a correct implementation that passes the test cases given at the bottom of this page. What appears below is an incorrect implementation it passes some of the test cases, but does not pass the others. def onlyevens(listofints): """ returns a list containing only the even numbers from a list of ints (I've left out the rest of the docstring to save space on the exam) """ if type(listofints)!=list: return False newlist = [] for item in listofints: if type(item)!=int: return newlist if listofints[0] % 2 == 0: newlist = newlist + [item] return newlist Your job: for each of the test cases shown, indicate whether the test passes or fails by placing a check in front of either the word passed or failed. In addition, if the test fails, fill in the blank with what the function returns instead of what was expected. The first two are done for you as an example of what I'm looking for. Test case For each row, check either the passed or failed column, If you check the failed column, fill in the blank with what you got instead of the expected value. check_expect("onlyevens test 1",onlyEvens('1'),False) _ passed failed: expected False, but got: check_expect("onlyevens test 2",onlyEvens(['a','b']),False) passed _ _ failed: expected False, but got: [ ] check_expect("onlyevens test 3",onlyEvens([]),[]) passed failed: expected [], but got: check_expect("onlyevens test 4",onlyEvens([1,2,3,4,5]),[2,4]) check_expect("onlyevens test 5",onlyEvens([1]),[]) check_expect("onlyevens test 6",onlyEvens([1,3]),[]) check_expect("onlyevens test 7",onlyEvens([3,2]),[2]) check_expect("onlyevens test 8",onlyEvens([2,3,4]),[2,4]) passed passed passed passed passed failed: expected [2,4], but got: failed: expected [], but got: failed: expected [], but got: failed: expected [2], but got: failed: expected [2,4], but got:

4 3. (12 pts) Rewrite each of the boolean expressions below as an equivalent expression that does not use the not operator. not (t > 0) Expression Equivalent Expression without not operator not (type(x)==str and len(x)<10) not ( type(x)==int or type(x)==float) (not a==0) and (not b*2-4*a*c < 0)

5 4. (20 pts) Write a Python function called letlist with a single parameter called listofstr that takes a list of strings, and returns a new list, where each string is replaced with the first letter of that string. If any item in the list is not a string or is an empty string, or if the parameter to the function is not a list, return the boolean value False. See the test cases for examples. For purposes of this this exam, is is not required to put a "docstring" or header comment on your function. Your function should pass these test cases: check_expect("letlist test 1",letList('1'),"error") check_expect("letlist test 2",letList(['a','b']),['a','b']) check_expect("letlist test 3",letList([]),[]) check_expect("letlist test 4",letList(['Univ','Calif']),['U','C']) check_expect("letlist test 5",letList(['Computer','Science']),['C','S']) check_expect("letlist test 6", letlist(['fouled','up','beyond','all','recognition']), ['F','U','B','A','R']) check_expect("letlist test 7",letList(['Spaghetti']),['S']) check_expect("letlist test 8",letList(['for','the','win']),['f','t','w']) check_expect("letlist test 9",letList(['for','the', 42,'doh!']),"error") check_expect("letlist test 10",letList(['for','the', '','doh!']),"error") You do not need to write the check_expect function, or recopy the test cases.

6 5. (10 pts) Write a Python function whereswaldo that takes a parameter alist, and returns -1 if the parameter is not a list, is an empty list, or if the string "Waldo" does not appear in the list. If the string "Waldo" does appear in the list, return the index of the first place that Waldo appears. See the test cases for examples. For purposes of this this exam, is is not required to put a "docstring" or header comment on your function. Hint: use a for loop such as for i in range(len(alist)): to search for an occurence of Waldo. Another Hint: we didn't say anything about requiring everything in the list to be a string. Look carefully at test case 10 and make sure your answer passes it as well. check_expect("whereswaldo test 1",wheresWaldo('1'),-1) check_expect("whereswaldo test 2",wheresWaldo(["he's","not","here"]),-1) check_expect("whereswaldo test 3",wheresWaldo([]),-1) check_expect("whereswaldo test 4",wheresWaldo(['My','friend','Waldo']),2) check_expect("whereswaldo test 5",wheresWaldo(['Hi','Waldo']),1) check_expect("whereswaldo test 6",wheresWaldo(['Have','you','met','Waldo']),3) check_expect("whereswaldo test 7",wheresWaldo(['Waldo']),0) check_expect("whereswaldo test 8",wheresWaldo(['Waldo','Waldo','Waldo']),0) check_expect("whereswaldo test 9",wheresWaldo(["Here's","a","Waldo","there's","a","Waldo"]),2) check_expect("whereswaldo test 9",wheresWaldo(["lowercase","waldo","can't","be","found"]),-1) check_expect("whereswaldo test 10",wheresWaldo([2,4,6,8,"who","do","we","appreciate","Waldo"]),8) You do not need to write the check_expect function, or recopy the test cases.

7 6. In your reading assignment for homework H10 there was a discussion of something called the runtime stack. We also discussed this in lecture. As you may recall, the run-time stack has stack frames that keep track of function calls. a. (2 pts) What is the event that causes a frame to be added to the stack? b. (2 pts) What is the event that causes a frame to be removed from the stack? c. (3 pts) Suppose we are running a Python program written by Chris. At a certain point in the program, we take a snapshot of the run-time stack and it looks like the picture shown below: we have a stack with frames for main, and functions called gaviota() and surf(). What do you know for sure about the relationship between the functions gaviota() and surf() in Chris' program just by looking at the picture of the stack? d. (3 pts) Now suppose we have a completely different Python program written by Pat. Pat's program also happens to contain functions called gaviota() and surf(), but other than that, the two programs don't necessarily have anything in common. Here is a snapshot of the stack from Pat's program. What can we conclude from this snapshot about the relationship between functions gaviota() and surf() in Pat's program and how it is different from what we saw in Chris' program?

8 7. (5 pts) When we open a file in Python, we can write a line of code like this: infile = open('students.txt','r') Or we may write a line of code like this: infile = open('students.txt','w') Describe what happens when you use the 'r', vs. what happens when you use the 'w'.

9 8. (5 pts) It is four years in the future and you are at your first real-world job after graduation. A coworker is having difficulty with a piece of software that she wrote, and asks you to take a look. She says: I don't understand it I'm expecting 1500 lines of output, but I'm only seeing the first 700 or 800. I can see that the code is writing all of the data, so I don't understand why it isn't showing up in my output file. You flash back to a discussion in your CS8 class about "buffering", and how it relates to writing data to files and the solution to your co-workers problem becomes clear to you. What do you suggest to your co-worker about the source of the problem, and what do you suggest the she try in order to address the problem?

10 End of Exam Total Points: 100