Duration - 3 hours Student Number: CSC 108H1Y 2013 Final Exam. Aids allowed: none

Transcription

1 University of Toronto Faculty of Arts and Science August 0 Examinations CSC 08HY 0 Final Exam Duration - hours Student Number: Aids allowed: none Last Name: Lecture Section: L50 First Name: Instructor: Jonathan Lung Do not turn this page until you have received the signal to start. (Please fill out the identification section above, write your name on the back of the test, and read the instructions below.) Reminder: You must achieve at least 40% on this exam in order to pass the course. Good Luck! This exam consists of 8 questions on pages (including this one). When you receive the signal to start, please make sure that your copy is complete. Comments are not required except where indicated, although they may help us mark your answers. They may also get you part marks if you can t figure out how to write the code. No error checking is required: assume all user input and all argument values are valid. If you use any space for rough work, indicate clearly what you want marked. # : # : # : Total Pages =

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3 E xam Summer 0 Question. [5 m a r k s ] Part (a) [ m a r k ] What is the name of the programming language we used in CSC08 this term? Part ( b ) [ m a r k ] What do we use CamelCase for? Part (c) [ m a r k ] When is the only time variables defined outside a function should be accessed? Part (d) [ m a r k s ] There are at least five things wrong, stylistically, with the following piece of code. Name two of them. There is a p e n a l t y fo r g u e s s i n g. AGE.GAP = if age > : 4 x = AGE_GAP+age 5 # Print x 6 print ( x ) Question. [4 m a r k s ] Part (a) [ m a r k ] The value 0 is has type in t. W hat is the type of 0.0? Part ( b ) [ m a r k ] If s t is the string 'H e llo, why does line one below cause an error but line two below does not? s t [0] = h st = h ' + st[i:] Page of

4 E xam Summer 0 Part (c) [ m a r k ] W hat is the value of var after running all the lines of code directly below? var = 0 var = var var = var Part (d) [ m a r k ] W hat is the value of var after running all the lines of code directly below? var = 0 var = 0 var = var var = var Part ( e ) [ m a r k ] What is printed to the screen by the code below? Assume it is not being run in the shell. def mystery(oooh, scary): oooh = oooh + scary return oooh oooh = 5 myst e r y (oooh, 5) p r i n t (oooh) Part (f) [ m a r k ] What is printed to the screen by the code below? Assume it is not being run in the shell. def myst e r y (): p r i n t ( hello ') return 'csc p r i n t ( 08 ) mystery () 4 P art (g) [ m a r k ] How many parameters does the function below have? def mystery(varl, var, var): magic = varl ** var voodoo = magic + len(var) return magic + voodoo Page of

5 E xam Summer 0 Part (h) [ m a r k s ] Assume the random module has been imported (help for the module is at the end of the exam). Generate a random integer between -00 and 00 (inclusive). Next, print two things to the screen (one on each line): the original random number and the absolute value of the random number Part (i) [ m a r k ] Consider the following function headers and type contracts: def moogah(x, y, z ) : ' ' (int, str, float) -> s t r def f r o o b l e ( x ) : ' ' ' (float) -> float ''> def m a r g h ( x, y ) : " (float, bool) -> b o o l " p = moogah(, 'f, 7.0) q = bazzle(8, f r o o b l e (9.6), p) print(margh(frooble (6), q)) If the following code runs without errors, what is the type contract for bazzle? p = moogah(, f, 7.0) q = bazzle(8, f r o o b l e (9.6), p) print(margh(f r o o b l e (6), q)) Part (j) [4 m a r k s ] Which of the following are statements and which are expressions? In each row, put a checkmark in only one of the two columns to indicate your answer. There is a penalty for guessing. Code Statement Expression < var sib lin g s = b ro th ers + s is t e r s w hile True: i f count < 0: ab s(d istan c e ) re tu rn 5 H e llo Page 4 of

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7 E xam Summer 0 Question. [5 m a r k s ] Part (a) [ m a r k ] Call the function below so that it returns False. def my_func(varl, var): return varl > 5 or len(var) < 5 Part (b) [ m a r k ] What is the purpose of = and what is the purpose of ==? Part (c) [ m a r k s ] For each of Moogah!, Nerts!, Oops!, Top!, Ruh ro!, and Plz!, give a value of var that will result in the string being printed out. If no value of var will result in that string being printed out, write not possible. if var > 5: p rint( 'Moogah! ) elif var < 5: print( N e r t s! ) if var < 5: p r i n t ( T o p! ) elif var > 0: p r i n t ( O o p s! ) else : p rint( Ruh ro! ) if var < 0: print( Plz! ) String Moogah! N e rts! Oops! Top!' Ruh r o! ' P lz! Value of var Page 5 of

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9 E xam Summer 0 Question 4. [5 m a r k s ] Part (a) [ m a r k ] Write a block of code that prints out the integers from up to and including 00, one per line. Part ( b ) [ m a r k ] What value(s) does the following function return? def mystery (): for ch in h e l l o : if ch in aeiou : 4 return ch P art (c) [ m a r k ] Write a function named re p e a t that returns the string 'h e llo repeated 00 times ( h e llo h e llo h e llo Do not use string multiplication ( h e llo * 00). Part (d) [ m a r k ] Write a program that prompts the user to enter text from the keyboard until the user types the word ' q u it (without quotes) on a line by itself. Part (e) [ m a r k ] What is the output of the function below? Clearly indicate your answer. flag = False while flag: print("flag") 4 flag = True Page 6 of

10 Question 5. [0 m a r k s ] Part (a) [ m a r k ] Suppose the following code runs without error. What is the type of varl? v a r l ['5 ] = hello' E xam Summer 0 Part (b) [ m a r k ] What is the length of the list [ Mind, th e, gap ]? Your answer should be a number (not a call to a function). Part (c) [ m a r k ] What two indices can be used to access the last item in the list [ Mind, the, gap ]? Part (d) [ m a r k ] What is the length of the list [ [ Apple, Orange ], [ Banana, C at, Dance ]]? Your answer should be a number (not a call to a function). Part (e) [ m a r k ] Suppose st refers to a l i s t. Write a block of code that prints out all the items in st using a while-loop. Part (f) [ m a rk ] Suppose name_to_id refers to a d ie t. Write a block of code that prints out all the values in name_to_id using a for-loop. Page 7 of

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12 E xam Summer 0 Part (g) [4 m a r k s ] Which of the following will work on c if c is a list but fail if it is a tuple? In each row, put a checkmark in only one of the two columns to indicate your answer. There is a penalty for guessing. Code Works for tuples Fails for tuples p rin t( c [0]) c [0] = 5 C.popO c [ : : - l ] c.re v e rs e () len (c) fo r e in c: p rin t(e ) o If n +o Question 6. [6 m a r k s ] Part (a) [ m a r k ] Write the class definition for a class named Person whose superclass is object. Part (b) [ m a r k s ] Write the entire constructor method (without comments/docstrings) for Person. The constructor should require a name as an argument and assign it to an attribute name. The constructor should also initialize an attribute named age to 0. Part (c) [ m a r k ] Rewrite the constructor above s header such that the name argument is optional and, if unspecified, defaults to the string John Smith. Page 8 of

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14 Part ( d ) [ m a r k ] E xam Summer 0 Write some code that creates an instance of Person and assigns it to a variable named person Part (e) [ m a rk ] Write a method for Person so that the following behaviour would be achieved for a Person named John Smith: >>> print (person.age) 0 >>> p e r s o n.birthday() Happy birthday, John Smith! >>> print(parson.age) >>> p e r s o n.birthday() Happy birthday, John S m i t h! >>> print(person.age) Page 9 of

15 E xam Summer Q uestion 7. [0 m a r k s ] P a r t (a) [ m a r k s ] Complete the following function according to its docstring. def raise.prices(original_fare_type_to_prices, fare_type_to_increase): ( d i e t of str to float, diet of str to float) -> diet of str to float Modify and return the dictionary original_fare_type_to_prices by adding the corresponding fare difference in fare_type_to_increase. All fare types in fare_type_to_increase exist in original_fare_type_to_prices. >>> raise_prices({ student :.00, adult :.00, senior :.00, c h i l d : 0.75}, { s e n i o r : 0.0, adult': 0.5}) { student :.00, adult :.5, senior :.0, c h i l d : } P a r t (b) [4 m a r k s ] Complete the following function according to its docstring: def is_before(timel, time): ( s t r, str) -> boolean Return True iff the time timel occurs before the time time. Both times are specified as strings of the form hour:minute am/pm. For example, "5: am" and ":0 pm" would be valid times. Days start at midnight (:00 am). >>> is_before(":0 am", ":5 am") True >>> is_before("5:6 pm", "8:09 am") Fa Ise >>> is_before ("5:6 pm", "5:6 pm") False >) ) Page 0 of

16 Part (c) [4 m a r k s ] E xam Summer 0 Complete the following function according to its docstring. Yyou may assume the is_before function works and is in the same file as this function. def earliest_time(times):, (list of str) -> object Return the earliest time in times. >>> earliest_time ( [ : 5 p m, ':0 p m, ' : 5 0 p m ]) ':0 p m >>> earliest_time ([ :56 p m, : 0 8 a m ]) :08 a m >>> earliest_time([]) None > j i Part (d) [5 m a r k s ] Complete the following function according to its docstring. You may assume the is_bef ore and e arlie st_ tim e functions work and are in the same file as this function. def busses_by_route(arrival.times): ( l i s t of [list of strsj) -> d i d of str to list of strs Return a dictionary of route numbers to arrival times for a route in any order. The inner list of arrival_times contains the bus route numbers and the arrival time of the bus. >>> busses_by_route ( [ [ 9 6 Wilson, : 5 p m ], [ 6 5 Weston R d. N o r t h, : 0 p m ], [ 9 6 Wilson, : 5 0 p m ], [ 9 7 Yonge, 4 : 0 0 p m ], [ 6 5 West R d. N o r t h, :58 p m ] ] ) { 9 6 Wilson : [ : 5 p m, : 5 0 p m ], 6 5 Weston R d. N o r t h : [ : 0 p m, : 5 8 p m ], 9 7 Yonge : [ 4 : 0 0 p m ] } > ) > Page of

17 Part (e) [4 m a r k s] E xam Summer 0 Complete the following function according to its docstring. You may assume the is_bef ore, earliest_ tim e, and busses_by_route functions work and are in the same file as this function. def next.bus.by.route(arrival.times): ( l i s t of [list of strsj) -> diet of str to str 4 Return a dictionary of route numbers to next arrival time for a route. 5 The inner list of arrival_times contains route numbers and arrival times. 6 7 >>> busses.by_route ( [ [ 9 6 Wilson, ' : 5 p m ], 8 [ 6 5 Weston R d. North, : 0 p m ], 9 [ 9 6 Wilson, : 5 0 p m ], 0 [ 9 7 Yonge, 4 : 0 0 pm>], [ 6 5 West Rd. No r t h, : 5 8 p m ] ] ) { 9 6 Wilson : : 5 p m, 6 5 Weston R d. N o r t h : : 5 8 p m, Yonge : 4:00 p m } 5 Question 8. [5 m a r k s ] Part (a) [ m a r k s ] Complete the following function according to its docstring. def load(processor.usage, m emory_free, memory.used): ( f l o a t, int, int) -> float 4 Return the computer load given the processor_usage, memory_free, and 5 memory_used. The computer load is the maximum of the processor 6 usage and the percentage of memory used % is represented by the float >>> load (0.95, 8, 8) >>> load (0.0, 8, 8) >>> load (0.0,, 4) Page of

18 E x a m Summer Part (b) [4 m a r k s] In a computer system that needs to be responsive (for example, computers that run websites), a computer that isn t particularly busy (it is idle) should respond to requests. For this question, you may assume the Computer class has a method called loado that requires no arguments when called and that returns the Computer s load. Complete the following function according to its docstring. def first_idle(computers): '''(list of Computers) -> Computer Return the first Computer in computers that is idle. An idle computer is one that has a load of below 0% (0.). Return None if no Computer is idle. > J ) P a r t (c) [4 m a r k s ] Sometimes, no idle computers can be found and the least busy computer should respond instead. You may again assume that the Computer class has a method called loado that requires no arguments when called and that returns the Computer s load. Complete the following function according to its docstring. You may assume that the f ir s t_ id le function above works and is in the same file and that the load doesn t change while this function is executing. def first_responder(computers): ( l i s t of Computers) -> Computer Return the first Computer in from computers that is idle. If no Computer is idle, return any one of the Computers that have the lowest load. An idle computer, is one that has a load of below 0% (0. ). J ) J Page of

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20 E xam Summer P a r t (d) [5 m a r k s ] In a system that provides high reliability (for example, the space shuttle), there are backup systems that are all performing the same calculations and/or measurements. Sometimes, these disagree. However, to make sure all the computers are in the same state, they need to have any discrepancies fixed. For example, if there are three computers on a space shuttle and two of them decide that the shuttle is going too fast and one disagrees, the one that disagrees should have its vote modified so that its version of events matches the version of events the other systems have agreed upon. Complete the following function according to its docstring. def fix_discrepency(votes, v o t e s, votes): '(list of booleans, list of booleans, list of booleans) -> list of boo leans Each of votesl, votes, and votes is a list of votes (True or False) by a set of computers. If there is a disagreement, modify each of the input lists so that they contain the majority vote and return a copy of the decisions. Each of the input lists will be of the same length. >>> fix_discrepency([true, False, True, False, True], [True, True, True, False, True], [True, False, True, False, False]) [True, False, True, False, True], )> > Page 4 of

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22 E xam Summer Part (e) [5 m a r k s] Complete the following function according to its docstring. def strong_passwd(passed): """ (str) -> bool A strong password has a length greater than or equal to 6, contains at least one lowercase letter, at least one uppercase letter, and at least one digit. Return True iff passwd is considered strong. >>> strong_passwd( I < c s c l O S ) True UII fl Part (f) [5 m a r k s ] On computer systems such as CDF, passwords are stored in a file named /etc/passw d. Each line in the file looks something like this: username:passw ord:full name:account enabled where account enabled is one of enabled or disabled. None of the usernames, passwords, or full names are permitted to contain colons (:). Complete the following function according to its docstring. For this question, you may assume the strong.passwd function described above works. def disable_bad_accounts(filtered_passwd_file): ( f i l e open for writing) -> None Writes all the accounts in /etc/passwd into filtered_passwd_file, but marking any enabled accounts as disabled if they do not have a strong password. Any previously disabled accounts remain disabled, even if they have strong passwords. The filtered_passwd_file is written to disk before this function returns. ) ) } Page 5 of

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24 EXAM Summer 0 This space intentionally left blank for extra space for answering questions, rough work, and drawings of turtles. Page 6 of

25 EXAM Summer 0 This space intentionally left blank for extra space for answering questions, rough work, and drawings of top hat-/monocle-wearing pigs. Page 7 of

26 E xam Summer 0 ass str(object) str(object ) -> str st r(bytes_or_buffer[, encoding!!, errors]]) -> str Create a new string object from the given object. If encoding or errors is specified, then the object must expose a data buffer that will be decoded using the given encoding and error handler. Otherwise, returns the result of o b j e c t. str () (if defined) or repr ( ob j e ct ). encoding defaults to s y s.g e t defaultencoding(). errors defaults to s t r i c t. Methods defined here: count (...) S.co u n t (sub [, start[, end]]) -> int Return the number of non - overlapping occurrences of substring sub in string S[st a r t :end]. Optional arguments start and end are interpreted as in slice notation. e ndswith(...) S.e n dswith(suffix [, start [, end]]) -> bool Return True if S ends with the specified suffix, False otherwise. With optional start, test S beginning at that position. With optional end, stop comparing S at that position, suffix can also be a tuple of strings to try. f ind (...) S.find(sub[, start[, end]]) -> int Return the lowest index in S where substring sub is found, such that sub is contained within S [ s t a r t :end]. Optional arguments start and end are interpreted as in slice notation. Return - on failure. isalnum (...) S. i s a l n u m O -> bool Return True if all characters in S are alphanumeric and there is at least one character in S, False otherwise. isalpha (...) S. i s a l p h a Q -> bool Return True if all characters in S are alphabetic and there is at least one character in S, False otherwise. isdigit (...) S. i s d i g i t O -> bool Return True if all characters in S are digits and there is at least one character in S, False otherwise. islower (...) S. i s l o w e r O -> bool Return True if all cased characters in S are lowercase and there is at least one cased character in S, False otherwise. isnumeric(...) S.isnumeric() -> bool Return True if there are only numeric characters in S, False otherwise. i sspace(...) S. i s s p a c e O -> bool Return True if all characters in S are whitespace and there is at least one character in S, Page 8 of

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28 E xam Summer 0 False otherwise. isupper (...) S. i s u p p e r Q -> bool Return True if all cased characters in S arc uppercase and there is at least one cased character in S, False otherwise. j oin (...) S.j o i n (iterable) -> str Return a string which is the concatenation of the strings in the iterable. between elements is S. The separator just (...) S.ljust(width [, fillchar]) -> str Return S left- justified in a Unicode string of length width. Padding is done using the specified fill character (default is a space). lower (...) S.l o w e r () -> str Return a copy of the string S converted to l o w e rcase. lstrip (...) S.l s t r i p ( [chars]) -> str Return a copy of the string S with leading whitespace removed. If chars is given and not None, remove characters in chars instead. part it ion (...) S.partition(sep) -> (head, s e p, tail) Search for the separator sep in S, and return the part before it, the separator itself, and the part after it. If the separator is not found, return S and two empty strings. replace (...) S.rep l a c e ( o l d, new[, count]) -> str Return a copy of S with all occurrences of substring old replaced by new. argument count is given, only the first count occurrences are replaced. If the optional rf ind (...) S.rfi n d (sub [, start [, end]]) -> int Return the highest index in S where substring sub is found, such that sub is contained within S [ s t a r t :end]. Optional arguments start and end are interpreted as in slice notation. Return - on failure. rindex (...) S.r i n d e x (sub [, start [, end]]) -> int Like S. r f i n d O but raise ValueError when the substring is not found. rjust (...) S.rjust(width [, fillchar]) -> str Return S right-justified in a string of length width. Padding is done using the specified fill character (default is a space). rpartit ion (...) S.rpartition(sep) -> (head, sep, tail) Search for the separator sep in S, starting at the end of S, and return the part before it, the separator itself, and the part after it. If the separator is not found, return two empty strings and S. Page 9 of

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30 E xam Summer 0 rsplit (...) S.r s p l i t (sep = None, maxsplit=-l) -> list of strings Return a list of the words in S, using sep as the delimiter string, starting at the end of the string and working to the front. If maxsplit is given, at most maxsplit splits are done. If sep is not specified, any whitespace string is a separator. rstrip (...) S.r s t r i p ( tchars]) -> str Return a copy of the string S with trailing whitespace removed. If chars is given and not None, remove characters in chars instead. split (...) S.s p l i t (sep = None, maxsplit=-i) -> list of strings Return a list of the words in S, using sep as the delimiter string. If maxsplit is given, at most maxsplit splits are done. If sep is not specified or is None, any whitespace string is a separator and empty strings are removed from the result. splitlines(...) S.s pli t l i n e s ([keepends]) -> list of strings Return a list of the lines in S, breaking at line boundaries. Line breaks are not included in the resulting list unless keepends is given and true. startswith(...) S.startsw i t h ( p r e f i x [, start[, end]]) -> bool Return True if S starts with the specified prefix. False otherwise. With optional start, test S beginning at that position. With optional end, stop comparing S at that position, prefix can also be a tuple of strings to try. strip (...) S.s t r i p ([chars]) -> str Return a copy of the string S with leading and trailing whitespace removed. If chars is given and not None, remove characters in chars instead. s w apcase(...) S. s w a p c a s e Q -> str Return a copy of S with uppercase characters converted to lowercase and vice versa. title (...) S.t i t l e () -> str Return a titlecased version of S, i.e. words start with title case characters, all remaining cased characters have lower case. upper (...) S. u p p e r () -> str Return a copy of S converted to uppercase. zf ill (...) S.zfill(width) -> str Pad a numeric string S with zeros on the left, to fill a field of the specified width. The string S is never truncated. Page 0 of

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32 E xam Summer 0 class list(object) I l i s t O -> new empty list Il i s t (iterable) -> new list initialized from i terable s items I I Methods defined here: I append (...) L.a ppend(object) -> None -- append object to end I I clear (...) L. c l e a r () -> None -- remove all items from L I I copy (...) L. c o p y O -> list -- a shallow copy of L I I count (...) I L.count(value) -> integer return number of occurrences of value I I extend (...) I L.extend(iterable) -> None -- extend list by appending elements from the iterable I I index (...) I L.i ndex(value, [start, [stop]]) -> integer -- return first index of value. Raises ValueError if the value is not present. I I insert (...) L.i nsert(i n d e x, object) -- insert object before index I I pop (...) I L.p o p ([index]) -> item -- remove and return item at index (default last). I Raises IndexError if list is empty or index is out of r a n g e. I I remove (...) I L.r emove(value) -> None -- remove first occurrence of value. Raises ValueError if the value is not p r e s e n t. I I reverse (...) L. r e v e r s e () -- reverse *IN PLACE* I I sort (...) I L.sort(key=None, reversa=false) -> None -- stable sort *IN PLACE* class diet(object) diet () -> new empty dictionary diet(mapping) -> new dictionary initialized from a mapping o b j e c t s (key, value) pairs d i e t (iterable) -> new dictionary initialized as if via: d = -O for k, v in iterable: d[k] = v diet(**kwargs) -> new dictionary initialized with the name=value pairs in the keyword argument list. For example: dict(one=l, two=) Methods defined here: cl e a r (...) D. c l e a r () -> None. Remove all items from D. copy (...) D. c o p y O -> a shallow copy of D fromkeys (...) diet.fromkeys (S [, v ] ) -> New diet with keys from S and values equal to v. v defaults to None. get (...) D.get(k[,d]) -> D[k] if k in D, else d. d defaults to None, items (...) D. i t e m s O -> a set-like object providing a view on D s items Page of

33 E xam Summer 0 keys (...) D. k e y s Q -> a set-like object providing a view on D s keys pop (...) D.pop(k[,d]) -> v, remove specified key and return the corresponding value. If key is not f o u n d, d is returned if g i v e n, otherwise KeyError is raised popit em (...) D. p o p i t e m O -> (k, v ), remove and return some (key, value) pair as a -tuple; but raise KeyError if D is empty. setdef ault (...) D.s e t d e f a u l t ( k [,d ] ) -> D.get(k,d), also set D[k]=d if k not in D update (...) D.update([E, ]**F) -> None. Update D from diet/ iterable E and F. If E present and has a.keys() method, does: for k in E: D[k] = E[k] If E present and lacks. k e y s O method, does: for (k, v) in E: D[k] = v In either case, this is followed by: for k in F: D[k] = F[k] values (...) D. v a l u e s () -> an object providing a view on D's values Help on module random: NAME random - Random variable g e n e r a t o r s. r a ndint(self, a, b) method of Random instance Return random integer in range [a, b ], including both end points. Page of E nd o f T e st

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