Assignment 1 (Python)

CptS355 - Assignment 1 (Python)
Overview
Weight: This assignment will count for approximately 5% of your final grade.
Due Date: Wednesday, Sept. 7 by 11:59PM
In this assignment you will explore use of some of the features of Python.
Turning in your assignment
Note the following directions carefully.
All the problem solutions should be placed in a single file named HW1.py. When you are done and certain that
everything is working correctly, turn in your file by uploading on the Assignment-1(Python) DROPBOX on
Blackboard (under AssignmentSubmisions menu). The file that you upload must be named HW1.py. Be sure to
include your name as a comment at the top of the file. Also in a comment, indicating whether your code is
intended for Unix/Linux or Windows -- programs' behavior may differ slightly between the two systems; your
code only has to work on one or the other. You may turn in your assignment up to 5 times. Only the last one
submitted will be graded. Please let the instructor know if you need to resubmit it a 6th time.
Implement your code for Python 3.
The work you turn in is to be your own personal work. You may not copy another student's code or work
together on writing code. You may not copy code from the web, or anything else that lets you avoid solving the
problems for yourself.
Grading
The assignment will be marked for good programming style (appropriate algorithms, good indentation and
appropriate comments -- refer to the Python style guide) -- as well as thoroughness of testing and clean and
correct execution. The points below add up to 95%. The remainign 5% will be for the thoroughness of your
testing. We will talk about the "testing requirements" in class.
Good python style favors for loops rather than while loops (when possible) for reasons discussed in class.
Also, code to do the same thing (or something easily parameterizable) at different points in a program
should not be duplicated but extracted into a callable function.
Turning in "final" code that produces debugging output is bad form, and points will be deducted. Here's a
trick. Near the top of your program write a debug function that can be turned on and off by changing a
single variable.
debugging = True
def debug(*s): if debugging: print(*s)
Where you want to produce debugging output use debug("This is my debugging output") instead of
print. (How it works: Using * in front of the parameter of a function means that a variable number of
arguments can be passed to that parameter. Then using *s as print's argument passes along those
arguments to print.)
Warmup -- makettable() and trans() -- 30%
The text of a message can be hidden by applying a translation function to each character.
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Define a function makettable(s1,s2) that returns a dictionary such that each character in s1 is mapped to the
character at the corresponding position in s2. You may assume that the characters in s1 are unique and that the
two strings are the same length. (When I say "you may assume X" it means that your code does not have to
check whether X holds or not). So for example, makettable('abcdefg', 'gfedcba') returns {'a': 'g',
'c': 'e', 'b': 'f', 'e': 'c', 'd': 'd', 'g': 'a', 'f': 'b'} Important note: throughout the class,
when I say a function returns a value, I do not mean that it prints the value. Please pay attention to the
difference.
Now, define a function trans(ttable, s). trans translates its string argument, s, according to its translation
table argument, ttable. Argument ttable is, of course, a dictionary returned by the makettable function, and
the result of trans is obtained by replacing each character, c, of s by ttable[c], if c is amongst the keys of the
ttable. If however c is not in ttable.keys() then it is unchanged in the output. This is all harder to describe
than to do! To easily look up k in dictionary, D, specifying that the same character is to be used if it is not present
as a key in the dictionary you can use
translation = D.get(k,k) # use help({}.get) to see more about get
The above trick with get to get a default value when a key is not present in a dictionary is important to
learn and use when appropriate. Points will be taken off for not using it when appropriate!
def makettable(s1,s2):
#write your code here
pass
def trans(ttable,s):
#write your code here
pass
Define a function testtrans() that minimally does the following (more testing code would be good.):
# function to test translation code
# return True if successful, False if any test fails
def testtrans():
ttable = makettable('abc', 'xyz')
revttable = makettable('xyz', 'abc')
tests = "Now I know my abc's"
answer = "Now I know my xyz's"
if trans(ttable, tests) != answer: return False
if trans(revttable, trans(ttable, tests)) != "Now I know mb abc's": return False
if trans(ttable,'') != '': return False
if trans(makettable('',''), "abc") != 'abc': return False
return True
histo() - 30%
Define a function, histo(s) computing the histogram of a given string. (Look up histogram in the dictionary if
you don't know what it means.) The histogram returned by the function is a list of characters in the input string s
each paired with its frequency. Characters must appear in the list ordered from most frequent to least frequent.
For example, histo('implemented') is [('e',3), ('m',2), ('d',1),('i',1), ('l',1), ('n',1),
('p',1), ('t',1)]. (Characters with the same frequency must appear in increasing alphabetical order.) To
implement the sorting you must use the python built-in function sorted. Do not write your own sorting code.
(Hint: help(sorted) and the Python documentation are your friends.)
Define a function testhisto() that tests your histo function, returning True if the code passes your tests, and
False if the tests fail. Hint: By now you should be familiar with using dictionaries and should be able to write a
function that builds the histogram in a single pass over the input string.
def histo(s):
#write your code here
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pass
def testhisto(ttable,s):
#write your code here
pass
testhisto()
digraphs() - 30%
A digraph is a pair of characters that occur adjacent to one another in a text. By convention we write each
digraph between a pair of '/' characters to make it easier to see where the blanks are. For example the digraphs
at the beginning of the first sentence of this section are /A /, / d/, /di/, /ig/, etc. Digraph frequency
counts are helpful in cryptological analysis of some ciphers.
Define a digraphs(s) function that returns a list containing the number of times each digraph occurs in string s.
Digraphs must be listed in alphabetical order. Again, use the built-in function sorted and do not write your
own sorting code. Digraphs that do not occur in the input (0 occurrences) should not be listed in the output.
Here is what the function might return on some hypothetical sample input:
[('/ </', 48), ('/ a/', 56), ('/ d/', 30), ('/ i/', 34), ('/ o/', 37),
('/ t/', 66), ('/. /', 31), ('/an/', 33), ('/co/', 47), ('/d /',38),
('/de/', 44), ('/e /', 83), ('/he/', 41), ('/in/', 53), ('/n /',40),
('/or/', 36), ('/r /', 32), ('/re/', 44), ('/s /', 44), ('/t /',36),
('/th/', 52), ('/to/', 42)
]
Define a test function, testdigraphs() to test your digraphs code using the same conventions as in the
previous problems.
Notes:
Split, Join and Slices
Suppose you have a list of words ["A", "smoky", "day", "on", "the", "Palouse"]. The join method on strings
concatenates the strings in a list, putting a copy of the string whose join method is used in between each of them.
For example:
uglyDayList = ["A", "smoky", "day", "on", "the", "Palouse"]
uglyDaySentence = ' '.join(uglyDayList) + '.'
uglyDaySentence
'A smoky day on the Palouse.'
Similarly, the split method on strings chops them up into a list, using a specified separator, which defaults to
whitespace.
uglyDaySentence.split()
['A', 'smoky', 'day', 'on', 'the', 'Palouse.']
Finally, slices are a handy way to get rid of unwanted things, like the last letter of a sentence, the trailing newline
character of a line read from a file, etc.
uglyDaySentence[:-1]
'A smoky day on the Palouse'
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Main program - 10%
So far we've just defined a bunch of functions in our HW1.py program. To actually execute the code, we need to
write the code for the "main" program. Unlike in C or Java, this is not done by writing a function with a special
name. Instead the following idiom is used. This code is to be written at the left margin of your input file (or at the
same level as the def lines if you've indented those.
if __name__ == '__main__':
...code to do whatever you want done...
For this assignment, we want to run all the tests, so your main should look like
if __name__ == '__main__':
passedMsg = "%s passed"
failedMsg = "%s failed"
if testttrans():
print ( passedMsg % 'testtrans' )
else:
print ( failedMsg % 'testtrans' )
# etc. for the other tests.
# notice how you are repeating a lot of code here
# think about how you could avoid that
Note that having your code pass your tests is not proof of the code's correctness -- but it is evidence. You can't
prove a program is correct by testing, though you can prove it is incorrect!
Cryptogram - 5% extra credit
Use your trans, histo, and digraph functions in an interactive python session to try to figure out the following
cryptogram. To make the functions available in the interactive session
from HW1 import *

If you haven't solved one of these before you may want to look on the web for hints on the relative frequencies
of letters and digraphs in the English language. You can use your functions to try out different possibilities and
get clues about the translation being used. (Digits and punctuation are not changed in these cryptograms.)
ZYX WVWUTSZRVQ VP OUNMXLX WKZYVQL WNXLXQZTK XLZSOTRLYXJ RQ
ZYX WSNI RL ZYX NXLUTZ VP SHHRJXQZST SQJ/VN RQZXQZRVQST NXTXSLXL OK
WXZ VGQXNL. ZYXLX RQZNVJUHZRVQL HSQ YSFX JXFSLZSZRQE HVQLXDUXQHXL ZV
VUN XHVLKLZXM. OUNMXLX WKZYVQL YSFX OXXQ PVUQJ ZV PXXJ VQ S GRJX
FSNRXZK VP MSMMSTL SQJ ORNJL RQ ZYX XFXNETSJXL-XFXQ ZYX VHHSLRVQST
STTRESZVN! OK WNXKRQE VQ QSZRFX GRTJTRPX, SQJ HVMWXZRQE GRZY VZYXN
QSZRFX WNXJSZVNL, WKZYVQL SNX LXNRVULTK RMWSHZRQE ZYX QSZUNST VNJXN
VP LVUZY PTVNRJS'L XHVTVERHST HVMMUQRZRXL. ZYX HVQZRQUXJ
WNVTRPXNSZRVQ VP OUNMXLX WKZYVQL-SQJ ZYX HVQZRQUXJ RQZNVJUHZRVQ VP
QXG PVNXREQ LWXHRXL-HSQ PUNZYXN ZYNXSZXQ MSQK VP ZYX XQJSQEXNXJ
WTSQZL SQJ SQRMSTL GX'NX GVNIRQE JRTREXQZTK
ZV WNVZXHZ. (GGG.QWL.EVF/XFXN/QSZUNXLHRXQHX/OUNMXLXWKZYVQLRQZNV.YZM)
LMYNHINSW LV WTR LLI LRWORRX 1969 NXH 1974, FJVQXG IQMIKS ONS
IYXIRQERH, OMQWWRX, NXH URMFYMZRH LV QWS ZRZLRMS GMNTNZ ITNUZNX, DYTX
IJRRSR, WRMMV GQJJQNZ, RMQI QHJR, WRMMV DYXRS, NXH ZQITNRJ
UNJQX. JYYSRJV SWMKIWKMRH NS N SPRWIT STYO, LKW OQWT NX QXXYENWQER
SWMRNZ-YF-IYXSIQYKSXRSS NUUMYNIT (NQHRH LV GQJJQNZ'S NXQZNWQYX), QW
UKSTRH WTR LYKXHNMQRS YF OTNW ONS NIIRUWNLJR QX SWVJR NXH IYXWRXW. N
SRJF-IYXWNQXRH IYZRHV WRNZ MRSUYXSQLJR FYM LYWT OMQWQXG NXH URMFYMZQXG
WTRQM OYMP, WTR UVWTYXS TNH IMRNWQER IYXWMYJ OTQIT NJJYORH WTRZ WY
RCURMQZRXW OQWT FYMZ NXH IYXWRXW, HQSINMHQXG MKJRS YF WRJREQSQYX
IYZRHV. WTRQM QXFJKRXIR YX LMQWQST IYZRHV TNS LRRX NUUNMRXW FYM VRNMS,
OTQJR QX XYMWT NZRMQIN, QW TNS IYJYKMRH WTR OYMP YF IKJW URMFYMZRMS
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FMYZ WTR RNMJV RHQWQYXS YF SNWKMHNV XQGTW JQER WTMYKGT WY ZYMR MRIRXW
NLSKMHQSW WMRXHS QX WRJREQSQYX IYZRHV. "UVWTYXRSBKR" TNS RXWRMRH WTR
RXGJQST JRCQIYX NS N MRSKJW.
Hint: use your makettable function to gradually build better and better translations between the uppercase
cryptogram characters to lowercase plaintext characters to make it visually apparent which characters have been
translated. Note numbers and punctuation in the cryptogram will appear unchanged in the answer.
Put your answer at the end of your HW1.py file in the form of an assignment of a triple-quoted string to the
variable thisIsTheCryptogramAnswer.
thisIsTheCryptogramAnswer = """
write your answer here
"""