CSE 130 - Programming Assignment #6

Python

130 points

(see submission instructions below)

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(Programming Assignment #6 FAQ)

Note: To download and install Python version 3.6.x on your home machines see this page. Remember that this is only to enable you to play with the assignment at home: The final version turned in must work on the ACS Linux machines. While you can use Windows to begin working with Python, the code you turn in must be that required for the Linux environment.

Integrity of Scholarship

University rules on integrity of scholarship will be strictly enforced. By completing this assignment, you implicitly agree to abide by the UCSD Policy on Integrity of Scholarship described in the Academic Regulations, in particular "all academic work will be done by the student to whom it is assigned, without unauthorized aid of any kind."

You are expected to do your own work on this assignment; there are no group projects in this course. You may (and are encouraged to) engage in general discussions with your classmates regarding the assignment, but specific details of a solution, including the solution itself, must always be your own work. Incidents that violate the University's rules on integrity of scholarship will be taken seriously: In addition to receiving a zero (0) on the assignment, students may also face other penalties, up to and including, expulsion from the University. Should you have any doubt about the moral and/or ethical implications of an activity associated with the completion of this assignment, please see the instructors.

Code Documentation and General Requirements

Code for all programming assignments should be well documented. A working program with no comments will receive only partial credit. Documentation entails providing documentation strings for all methods, classes, packages, etc., and comments throughout the code to explain the program logic. Comments in Python are preceded by # and extend to the end of the line. Documentation strings are strings in the first line of a function, method, etc., and are accessible using help(foo), where foo is the name of the method, class, etc. It is understood that some of the exercises in this programming assignment require extremely little code and will not require extensive comments.

While few programming assignments pretend to mimic the "real" world, they may, nevertheless, contain some of the ambiguity that exists outside the classroom. If, for example, an assignment is amenable to differing interpretations, such that more than one algorithm may implement a correct solution to the assignment, it is incumbent upon the programmer to document not only the functionality of the algorithm (and more broadly his/her interpretation of the program requirements), but to articulate clearly the reasoning behind a particular choice of solution.

Assignment Overview

The overall objective of this assignment is to introduce you to Python. Emphasis will be placed on text and string manipulations and should use some of Python's facilities for iterating over structures. The assignment is spread over three python files misc.py, vector.py, test.py and one text file news.txt that you need to download. The first two files contain several skeleton Python functions, with missing bodies, i.e. expressions, which currently contain the text raise Failure("to be written") or pass. Your task is to replace the text in those files with the the appropriate Python code for each of those expressions. An emphasis should be placed on writing concise, easy to read code.

Assignment Testing and Evaluation

Your functions/programs must compile and/or run on a Linux ACS machine (e.g. ieng6.ucsd.edu), as this is where the verification of your solutions will occur. While you may develop your code on any system, ensure that your code runs as expected on an ACS machine prior to submission. You should test your code in the directories from which the zip files (see below) will be created, as this will approximate the environment used for grading the assignment.

Most of the points, except those for comments and style, will be awarded automatically, by evaluating your functions against a given test suite. The third file, test.py contains a very small suite of tests which gives you a flavor of these tests. At any stage, by typing at the UNIX shell :

python3 < test.py | grep "130>>" > log

you will get a report on how your code stacks up against the simple tests.

The last (or near the bottom) line of the file log must contain the word "Compiled" otherwise you get a zero for the whole assignment. If for some problem, you cannot get the code to compile, leave it as is with the raise ..., with your partial solution enclosed below as a comment. There will be no exceptions to this rule. The second last line of the log file will contain your overall score, and the other lines will give you a readout for each test. You are encouraged to try to understand the code in test.py, and subsequently devise your own tests and add them to test.py, but you will not be graded on this.

Alternately, inside the Python shell, type (user input is in red):

>>> import test . . . 130>> Results: ... 130>> Compiled

and it should print a pair of integers, reflecting your score and the max possible score on the sample tests. If instead an error message appears, your code will receive a zero.

Submission Instructions

1. Create the zip file for submission

Your solutions to this assignment will be stored in separate files under a directory called pa6_solution/, inside which you will place the files: misc.py, vector.py . These two files listed are the versions of the corresponding supplied files that you will have modified. There should be no other files in the directory.

After creating and populating the directory as described above, create a zip file called <LastName>_<FirstName>_cse130_pa6.zip by going into the directory pa6_solution and executing the UNIX shell command:

zip <LastName>_<FirstName>_cse130_pa6.zip *

2. Test the zip file to check for its validity

Once you've created the zip file with your solutions, you will use the validate_pa6 program to see whether your zip file's structure is well-formed to be inspected by our grading system by executing the UNIX shell command:

validate_pa6 <LastName>_<FirstName>_cse130_pa6.zip
The validate_pa6 program will output OK if your zip file is well-formed and your solution is compiled. Otherwise, it will output some error messages. Before going to step 3, make sure that your zip file passes validate_pa6 program. Otherwise you get a zero for the whole assignment. If you have any trouble with this, refer to the instructions in step 1.

3. Submit the zip file via the `turnin_pa6` program

Once you've created the zip file with your solutions, you will use the turnin_pa6 program to submit this file for grading by going into the directory pa6_solution/ and executing the UNIX shell command:

turnin_pa6 <LastName>_<FirstName>_cse130_pa6.zip

The turnin_pa6 program will provide you with a confirmation of the submission process; make sure that the size of the file indicated by turnin_pa6 matches the size of your zip file. (turnin_pa6 is a thin wrapper script around the ACMS command turnin that repeats validation and ensures that the propper assignment name is passed). Note that you may submit multiple times, but your latest submission overwrites previous submissions, and will be the ONLY one we grade. If you submit before the assignment deadline, and again afterwards, we will count it as if you only submitted after the deadline.

Hints

Using .py Files

To load foo.py into python, where bar() is defined in foo.py do the following:

import foo foo.bar()

Modify foo.py, then to reload it:

from importlib import reload reload(foo) foo.bar()

If you use the following syntax instead, you have to restart python to reload it.

from foo import * bar()

Useful Links

Quirks / Features of Python

None doesn't print a line when it is the return value
None, 0, and [] all evaluate to false when used as a predicate.
Many objects can be iterated over with for loops, not just lists.

Problem #1: Warm-Up `(misc.py)`

(a) 15 points

Write a function closest_to(l,v) , which returns the element of the list l closest in value to v. In the case of a tie, the first such element is returned. If l is empty, None is returned. Once implemented you should get the following behavior at the Python prompt:

>>> from misc import * # this will load everything in misc.py >>> closest_to([2,4,8,9],7) 8 >>> closest_to([2,4,8,9],5) 4

(b) 15 points

Now, write a function make_dict(keys,vals) which takes a list of keys and a list of values and returns a dictionary (dict) pairing keys to corresponding values. Once you have implemented the function, you should get the following behavior at the Python prompt:

>>> make_dict(["foo","baz"],["bar","blah"]) {'foo': 'bar', 'baz': 'blah'} >>> make_dict([1],[100]) {1: 100}

(c) 30 points

Write a Python function word_count(filename) that takes a string, filename, and returns a dictionary mapping words to the number of times they occur in the file filename. For this function, a word is defined as a sequence of alphanumeric characters and underscore. All other characters should be ignored. Words should be returned in lower case, and case should be ignored when counting occurrences. Once you have implemented the function, you should get the following behavior at the Python prompt:

>>> word_count("news.txt") {'all': 2, 'code': 2, 'gupta': 1, 'results': 1, 'four': 1, 'edu': 2, ...}

Problem #2: Vector class `(vector.py)`

The Vector class that you will implement will be a fixed length vector which implements a variety of operations.

(a) 10 points

Add a constructor to the Vector class. The constructor should take a single argument. If this argument is an int or an instance of a class derived from int, then consider this argument to be the length of the Vector. In this case, construct a Vector of the specified length with each element is initialized to 0.0. If the length is negative, raise a ValueError with an appropriate message. If the argument is not considered to be the length, then if the argument is a sequence (such as a list), then initialize with vector with the length and values of the given sequence. If the argument is not used as the length of the vector and if it is not a sequence, then raise a TypeError with an appropriate message.

Next implement the __repr__ method to return a string of python code which could be used to initialize the Vector. This string of code should consist of the name of the class followed by an open parenthesis followed by the contents of the vector represented as a list followed by a close parenthisis. Once you have implemented the function, you should get the following behavior at the Python prompt:

>>> from vector import * >>> Vector(3) Vector([0.0, 0.0, 0.0]) >>> Vector([4.5, "foo", 0]) Vector([4.5, 'foo', 0]) >>> Vector(0) Vector([]) >>> Vector(-4) Traceback (most recent call last): File "<stdin>", line 1, in ? File "vector.py", line 14, in __init__ raise ValueError("Vector length cannot be negative") ValueError: Vector length cannot be negative

(b) 10 points

Implement the functions __len__ and __iter__ in Vector. The function __len__ should return the length of the Vector. The function __iter__ should return an object that can iterate over the elements of the Vector. This is most easily done using yield(). See here for more information.