Lab 5: Structured Programming II

Transcription

1 5.1 Introduction Lab 5: Structured Programming II Lab this week is going to focus on debugging, list comprehensions, and loading data from files. 5.2 Resources The additional resources required for this assignment include: 0 Books: Punch & Enbody 0 Pratt Pundit Pages: Python:Turtle 0 Lab Manual Appendices: None 5.3 Getting Started 1. Log into one of the PCs in the lab using your NET ID. Be sure it is set to log on to WIN. 2. In Windows: (a) Mount your CIFS drive - start a browser and point it to: Follow the instructions; for step 4, only the first bullet applies. (b) Start a browser and point it to: Check out the Using the PCs to Run Unix Programs Remotely section for how to get connected and make sure the connection is working. (c) Start Spyder. In the start menu, there is a group for Anaconda; Spyder is in that group. 3. In UNIX: (a) Change into your folder for EGR 103L, create a lab5 folder inside it, then switch into that folder: cd /EGR103 mkdir lab5 cd lab5 (b) Copy the tar file from Dr. G s space into your lab5 folder and expand the tar file: wget people.duke.edu/ mrg/egr103public/lab5files.tar tar -kxvf Lab5Files.tar (c) Make a personal copy of the lab report skeleton: cp -i Lab5Sample F18.tex lab5.tex 5 1

2 5.4 Ungraded You should look at, and if possible work on, 0 P&E Chapter 3 Exercises P&E Chapter 4 Exercises 1-22, 29-32, 37, 41, 48 For these ungraded problems, you can compare answers and processes with classmates. Do not share answers outside of those people currently taking the course. 5.5 Useful Information String and List functions 0 Some methods return values without impacting the original argument variable and others impact their arguments (and may not return anything). Since strings are immutable, methods that act on strings fall into the first category. 0 For strings, some of the methods that return new strings are capitalize, lower, swapcase, title, and upper. The methods do not change the original string but return a modified version of it based on the rules of the function. 0 Other commands that take a string and return information based on the string without changing the string are count, find, index, replace, and split. 0 Some methods that work with lists return values without changing the original list. These include count and index. 0 Finally, some methods that work on lists actually change the list. These include pop (which changes the list by removing an element and also returns the element popped out), remove (which removes the first element matching the argument of remove, does not return anything, and throws an error if there is no match). Debugging Introduction As you start writing more and more complicated codes, and as those codes rely more and more on functions, you need to learn more about how to debug code. Spyder includes tools to access some of the features of pdb, the Python debugger. These tools will allow you to step through a program, engage with the current environment (which is extremely helpful in debugging code inside a function), and even make temporary changes on the command line to see how those how the code works going forward. The debugging tools are the blue icons at the top of the Spyder window. First, you will want to go through an article, Debugging in Python, which was written in 2009 on a blog, Python Conquers the Universe. The post is at: https :// pythonconquerstheuniverse. wordpress. com /2009/09/10/ debugging -in - python / There are also some videos to help with debugging: quick demo on how to set and use a breakpoint. Be sure to save the file after setting a breakpoint demo using turtle drawings to show how to debug. Note: the program as given in the video will not always work with the latest version of Python or Spyder. Instead, a code that will work is in the files you copied this week. Spring 2018 APTs As mentioned in class Monday, you are going to be working on some of the APT (Algorithmic Problem-solving Testing) problems from Computer Science 101. You will be able to test the APTs yourselves and there s generally no reason not to get full credit for an APT problem. Please note - for these program, while you are allowed to import the math module, you are not allowed to give it a nickname. That is, if you want to use math, you can have the import math line and prepend math. in front of functions; you are not allowed to use import math as m. You cannot import numpy. 5 2

3 Turtles For part of this lab, you will be learning how to use turtle graphics to make a drawing. You will want to read along with Chapter 4 of the Downey online book. One quick note - for some reason, the current version of Spyder and Python generate an error every time a new turtle is created. For that reason, scripts will generally need to have the following to work: #%% Imports import t u r t l e #%% Generate window and t u r t l e wn = t u r t l e. Screen ( ) try : kasa = t u r t l e. Turtle ( ) except : kasa = t u r t l e. Turtle ( ) #%% Draw t h i n g s #%% Done drawing # This w i l l c l o s e the t u r t l e screen when you c l i c k on i t in Windows from sys import platform i f platform== win32 : wn. e x i t o n c l i c k ( ) The try...except structure seems redundant but it solves the feature of turtle creation working only every other time. This should generally be the wrapper of any turtle-based work. Note that you can issue turtle commands in the console - just remember when you create the turtle there is half a chance that you will get an error (it tells you that it is going to raise Terminator, then Terminator appears Experiments show that trying either sarah connor = t u r t l e. Turtle ( ) or john connor = t u r t l e. Turtle ( ) do not fix the issue. The following sub-sections will note changes or clarifications of the sections of the Downey book. Downey 4.1 The turtle module Instead of what is given on the page, your mypolygon.py script will look like: import t u r t l e wn = t u r t l e. Screen ( ) try : bob = t u r t l e. Turtle ( ) except : bob = t u r t l e. Turtle ( ) print ( bob ) from sys import platform i f platform== win32 : wn. e x i t o n c l i c k ( ) You will add code to the script after the print line but before the exitonclick line to make the square. 5 3

4 Downey 4.3 Exercises In each case, be sure to use the wrapper presented above around your script. Note that all of these functions should be defined in the mypolygon script. Downey 4.12 Exercises The solution scripts do not have the wrapper codes in them and will cause problems with Python and Spyder if run as-is. If you download the solution codes, be sure to add the wn = t u r t l e. Screen ( ) try : bob = t u r t l e. Turtle ( ) except : bob = t u r t l e. Turtle ( ) to the start of the main part of the code and change the end to: from sys import platform i f platform== win32 : wn. e x i t o n c l i c k ( ) 5.6 Assignment APT for Lab 5 For lab this week, you should work on and complete the following problems from: https :// www2.cs.duke. edu / courses / spring18 / compsci101 / apt / secure / Create a folder called APT in your CIFS EGR103 folder and put your files for this part of the assignment there. Please note - if you took CS 101 and have previously worked on these problems, you are allowed to re-submit your previous work but are highly encouraged to go back through the work you did 0 Problem Set 1: Gravity, Bogsquare 0 Problem Set 2: Laundry, DNAcgratio, PortManteau, RemoveMiddle 0 Problem Set 3: Bagels, ScoreIt, IsSpecial 0 Problem Set 4: MorseLikeCode (we ll talk about this one in lab) Please note - these are individual assignments. You can discuss your code with the TAs or the instructor but should work on your own. Also, some of these assignments may be active assignments for CS sharing solutions to active assignments with students in other classes is academically dishonest and deserving of engagement with the conduct board. After things are graded, comparing codes is a great way to learn. The first time you try to submit an APT for grading you will likely get an error that the file cannot be moved. Simply go back to the previous page, re-indicate what file you want to upload and which assignment you are hoping to try, and submit again. After you have completed all ten programs, click the check submissions link at the top of the page - a TA can go through and check the score for your ten problems. You will not need to submit these scripts with Lab 5, but they do need to be in your EGR103/APT folder. 5 4

5 5.6.2 Koch Curve The Koch curve, named for Helge von Koch, is a shape built using a recursive algorithm as follows - take a line segment and then as described on the Koch Snowflake page on Wikipedia: https :// en. wikipedia. org / wiki / Koch_snowflake (1) divide the line segment into three segments of equal length. (2) draw an equilateral triangle that has the middle segment from step 1 as its base and points outward. (3) remove the line segment that is the base of the triangle from step 2. The first application will create four equal-length segments. The recursive part is to then take each of those four segments and apply the above steps to those. This process can continue indefinitely. You are going to writing a script that will define a couple useful functions and then use them to generate a Koch curve based of a particular length and level. Your script will start with the following structure in the files you copied this week: #%% Imports import t u r t l e #%% Define f u n c t i o n s def koch curve ( t, length, l v l=0 ) : Draw Koch Curve o f given l ength and l e v e l i f l v l==0 : t. forward ( l e n gth ) # the r e s t i s yours to w r i t e def i n i t t u r t l e ( t ) : Set pen s i z e, speed, and c o l o r t. p e n s i z e ( 2 ) t. speed ( 0 ) t. c o l o r ( white ) #%% Main code i f s c r i p t i s run i f name == m a i n : wn = t u r t l e. Screen ( ) wn. c l e a r s c r e e n ( ) wn. b g c o l o r ( black ) try : kasa = t u r t l e. Turtle ( ) except : kasa = t u r t l e. Turtle ( ) # The r e s t i s yours to w r i t e from sys import platform i f platform== win32 : wn. e x i t o n c l i c k ( ) You will be writing a koch_curve function to generate a Koch curve. The function will have three inputs: a variable for the turtle, a variable for the line segment length, and a variable for the levels of recursion. To start, note that a level 0 Koch curve is merely a straight line of a given length. Your function has been started so that it moves the turtle forward by the specified length in cases where the level given is

6 Your code should create a curve that is 600 units wide and draw it going from left to right. The main part of your code should create the window and the turtle and then have the turtle start drawing at (-300, 0). You want to get there without the turtle actually drawing anything, however, so if your turtle s name is kasa, after you have created the turtle, use the commands: i n i t t u r t l e ( kasa ) kasa. penup ( ) kasa. s e t p o s i t i o n ( 300, 0 ) kasa. pendown ( ) This will set the turtle s size, speed, and color from the init_turtle function, then it will lift the pen before moving to the right location and putting the pen down. At this point, you could also add the command to create a level 0 curve with: koch curve ( kasa, 600 ) If you save and run this program, there should be a white line going from left to right in your Python Turtle Graphics window. Next, think about how to get from one level to the next. If someone asks for a level 1 Koch curve, that is going to be built of four level 0 Koch curves, each being one third of the given length and with turns between segments. Use a pen/pencil and paper to draw a Koch level 1 curve that is a total of 3 inches across. Note that each segment you draw will be 1 inch in length. Pay careful attention to how much you need to turn each time to head in the right direction. One you can do that on paper, you should be able to write the code for it. Your koch_curve for levels larger than 0 should include four different calls to the koch_curve function; these calls will each have the same shorter length and lower level than the original call. Re-read the paragraph above for a major hint on that. For this assignment, you can use whatever colors you want as long as the curve stands out from the background. The Pundit page has more information on colors. As you work on the code, you can use whatever color(s) you like for the line section(s) as long as it(they) contrast well with the background (which can also be the color of your choice). Once your program is working, use it to create a level 4 Koch curve. The way you will document your work this week will be to take a screen grab of the Python Turtle Graphics window. You will save the file and then upload it along with your Lab - that is, you will not be importing the picture in your lab document. There is more information on capturing the Python Turtle Graphics window on the Pundit page for Python:Turtle Based on P&E 4.46 For this problem, you are going to write a script that contains functions to process a word and then a phrase made up of words by encoding each word (almost) as described in the problem. There are several steps to performing this task - you should complete them one at a time and you should test your code every step of the way. Remember that you can put test code in the same scripts as your functions as long as you start that code with: i f name == m a i n : 0 First, note that the book has a small error in the encoding. If m were the 12th letter, that would mean a is zero and that you should in fact have the new number be 25-i. That s a little irrelevant in our case because your code is going to use ord() to get the numerical value of a character and chr() to get the character from an integer. Type: l i s t (map( ord, AZaz ) ) to see what Python thinks are the numerical values of those four letters. 0 Next, you are going to write a function whose job it is to take a single character, encode it as described in the book, and return the encoded character. Start this function with: def c o d e l e t t e r ( c h a r i n ) : and write code that assumes the char_in is a single letter string. For the moment, also assume that the character is a lower case letter. Figure out how to get your function to return the correctly encoded version of that single lower case letter. For example: 5 6

7 In [1]: code_letter ( c ) Out [1]: x In the main part of your code, you might want to run a loop that checks and prints out all the lower case numbers and their encoded letters. There are several ways to create this loop - one would be to loop over the numerical values of the letters and use ord() to convert the numbers to a letter. Write a loop that runs k through the numbers that represent lower case letters and put the following command in that loop: print ( chr ( k ), c o d e l e t t e r ( chr ( k ) ) ) 0 Now figure out how to deal with upper-case letters. The function should return upper-case letters if the original is in lower case. For example: In [1]: code_letter ( Q ) Out [1]: J You can either change your loop to go through just the upper-case letters, add a second loop to go through just the upper-case letters, or create an iterator including the lower-case and upper-case numbers. The latter is complicated by the fact that there is no + for the range command, but you can look at how: x = l i s t ( range ( 2, 10 ) ) + l i s t ( range ( 100, 110 ) ) to see how you might create a composite range. 0 Finally, if the input contains non-letter characters, the function should return the same non-letter character; add code to make this work: In [1]: code_letter ( ) Out [1]: To test your code, run your loop through the values 48 through 125; this represents all the numbers and letters and several symbols (which should remain unchanged). 0 Now that you are able to convert individual characters, you are going to write a second function that can convert entire strings. This function definition will come after the code_letter definition in your script. This function will take one required input - the old sentence - as well as an optional second input to determine if the old and new sentences should be printed on the screen. The function will return the encoded sentence. Start your function with: def code message ( o l d s e n t, show=0 ) : and before writing any more code, think about how you the human would use the code_letter to take a string and convert it to an encoded string one character at a time. You will want to build a string by appending the encoded characters. The good news is you do not have to worry about spaces between words - giving spaces to code_letter will automatically return spaces. Once you have this function completed, you can test it with: code message ( Let s Go Duke EGR 103 F a l l 2018, 1 ) and you should get: Let s Go Duke EGR 103 Fall 2018 Ovg h Tl Wfpv VTI 103 Uzoo 2018 Note the use of regular quotation marks to set off the input string since the apostrophe is a part of the string. Make sure that these tests are all in that if statement that will only run if you run the script as main. 0 To demonstrate how your code works, use the test_encoding script and pay careful attention to how it works - we will go over it in lab. The Coded.txt file will be a part of your lab report. 5 7

8 5.6.4 P&E 4.49 This problem is similar to the encoding problem, and you should thus break it down into parts. In a script called scrambler: 0 Define a function called scramble_word that you can assume takes a single word (i.e. letters only) as an input and returns the scrambled version. The scrambled version will start and end with the same letters as the original but the letters in the middle can be all mixed up. 0 The np.random.shuffle() function will be helpful here, but it only works on lists. If you were to want to scramble Pratt for example, you can slice the middle of the word to get a string m= rat but you cannot shuffle the letters with np.random.shuffle(m). You can shuffle a list of letters, however, so np.random.shuffle( list(m)) does work. Note that this command changes the list it is given it does not return anything. 0 After shuffling the interior letters, you can build the new word as a list and then convert that list to a string by using.join(). For example, look at how the following takes the letters sliced from Pratt and works to end with a string of shuffled letters: In [1]: x = rat In [2]: xlist = list (x) In [3]: xlist Out [3]: [ r, a, t ] In [4]: np. random. shuffle ( xlist ) In [5]: xlist Out [5]: [ a, r, t ] In [6]:. join ( xlist ) Out [6]: art Again - note that shuffle shuffles the entries in the list and changes that list - it does not return anything If you tried to get an output from line 4: In [7]: blah = np. random. shuffle ( xlist ) In [8]: print ( blah ) None 0 Test your function with one, two, and more than two letter words. Your tests should all be under a statement: i f name == m a i n : in your scrambler script. You can assume this function will only be getting words - no spaces, numbers, or punctuation marks. A quick test of your code might be to run the following loop: for k in range ( 20 ) : print ( scramble word ( AbcdefG ) ) If your code is working correctly, all 20 of the new words will start with A, end with G, and have various combinations of bcdef in the middle. 0 Now start a function called scramble_line that is going to take a line of text as an input, scrambles each word in that line of text, and returns a line of text now with the scrambled words. One easy way to split a line of text into individual words is to use the.split() function. This function acts on a string and returns a list of strings. The argument of the command is what character is used as the divider between strings in the original. The default is a space, though sometimes other characters might be useful depending on how you want to split things. Consider the following: 5 8

9 In [ 1]: all_ text = Gustafson, Michael Richard In [2]: all_text. split () Out [2]: [ Gustafson,, Michael, Richard ] In [3]: all_text. split (, ) Out [3]: [ Gustafson, Michael Richard ] (hint for a future APT and for this lab - that leading space in the second item can be removed with a convenient slice). 0 After you get a list of words, you should figure out how to get your scramble_line to scramble each word and then build a new string with the scrambled words. There should be spaces between the words, so you could get something like: In [ 1]: scramble_ line ( Duke University in Durham North Carolina ) Out [ 1]]: Dkue Unsritievy in Duahrm Ntroh Conlriaa 0 At present, this code does not handle punctuation. You will not be required to deal with punctuation except for items that come directly after a word (so periods, commas, colons, etc.). You will need to figure out how to check if a word ends with a non-letter. If it does, your program should store the non-letter, remove it from the word before sending the word to get scrambled, then return the non-letter to the end of the scrambled word. After you have this part working, you can test your code with an argument such as: In [1]: scramble_line ( Go Duke Where is Duke? Durham, North Carolina. ) Out [1]: Go Duke Whree is Dkue? Dahurm, Ntorh Coarnlia. You can program this to be dealt with either in the scramble_word code or in the scramble_line code. Again, think about what you the human would need to do if given something like Break Already? Python has a command to check letters called.isalpha() - note the following runs: In [1]: a. isalpha () Out [1]: True In [2]: aha. isalpha () Out [2]: True In [3]: aha. isalpha () Out [3]: False Again - for this you can assume that if there is any punctuation, it is at the end. about...well... don t. Don t worry 0 The test_scrambler code is already written. We wree gonig to have you wtrie it but ddiceed anigsat it. 0 You will include the results from the test code in the body of your lab report. 5 9