Assignment Lab #8 Solution

Assignment Objectives




By the end of this assignment you should be able to design, code, run and test original Python functions that solve program-ming problems involving file I/O, classes, and other Python concepts.




Getting Started




The assignments in this course require you to write Python code to solve computational problems. To help you get started on each assignment, we will give you a “bare bones” file with a name like lab8.py. These files will contain function stubs and a few tests you can try out to see if your code seems to be correct. Stubs are functions that have no bodies (or have very minimal bodies). You will fill in the bodies of these functions for the assignment. Do not, under any circumstance, change any class or function names that we have provided for you (or modify the parameter lists of those functions). The automated grading system will be looking for exactly those class and function names provided in lab8.py. Please note that the test cases we provide you in the bare bones files will not necessarily be the same ones we use during grading!




Directions




Complete the following assignment to the best of your ability. This assignment is worth a total of 20 points in all, divided between two classes, their methods, and two external functions. The automated grading system will execute your solution to each problem several times, using different input values each time. Each test that produces the correct/expected output will earn 1 point. You must earn at least 16 points (80%) in order to pass (receive credit for) this lab.




At the top of the lab8.py file, include the following information in comments, with each item on a separate line:




 
your full name AS IT APPEARS IN BLACKBOARD




 
your Stony Brook ID #




 
your Stony Brook NetID (your Blackboard username)




 
the course number (CSE 101)




 
the assignment name and number (Lab #8)




Each of your functions must use the names and parameter lists indicated in the starter code file. Submissions that have the wrong function names (or whose functions contain the wrong number of parameters) can’t be graded by our automated grading system, and may receive a grading penalty (or may not be graded at all).




Be sure to submit your final work as directed by the indicated due date and time. Late work will not be accepted for grading. Work is late if it is submitted after the due date and time.




Programs that crash will likely receive a grade of zero, so make sure you thoroughly test your work before submitting it.































CSE 101 – Lab #8 Page 1
A Very Fishy Problem




Previously in lecture, we discussed Python classes, which allow us to define our own data types that combine data (instance variables) and operations (instance methods). In this lab, we will use classes to create a virtual aquarium.




 
Start by completing the Fish class, which will represent a single fish in our aquarium. Every Fish has four attributes, represented as instance variables: its name, its species, its color, and its weight in ounces. A Fish also has the following methods (with the following headers):




__init__(self, name, species, color, weight)




This method creates four new instance variables for the current Fish, and assigns them the values of the last four method parameters. Remember that an instance variable’s name is always preceded by "self.", as in self.myData.




__repr__(self)




This method returns a string representing the current Fish. This string should include a crude fish symbol (<<) followed by the Fish’s name, color, and species in parentheses. For example:




<< (Topper, blue Guppy)




__lt__(self, other)




This method returns True if the current Fish’s weight is less than the other Fish’s weight instance variable, and False otherwise. Remember that Python does not protect instance variables from outside access, so you can directly refer to the weight instance variable from the other parameter.




kind(self)




This method returns the species of the current Fish.




 
Complete the createFish() function, which takes a single string argument in the form: species name color weight




where each field is separated by a single space (assume that the species and name are always single-word values). This function should create and return a new Fish object whose attributes are based on the contents of this string. Note that the fields of the string are in a slightly different order than the argument list of the Fish class, and that the “weight” value must be converted from a string to a float value before the new Fish is created.




 
We also need an aquarium to hold our fish. To do this, we need to define a second class, named Aquarium. An Aquarium has two instance variables: a list of Fish instances, and an integer representing the water capacity of the tank in gallons (each Fish requires 1 gallon of water). An Aquarium also has the following methods:




__init__(self, capacity)




This method creates a new instance variable that is an empty list; this list will eventually be filled with Fish objects. It also assigns its second parameter to a new instance variable representing the Aquarium’s total capacity in gallons.




__repr__(self)




This method returns a single string that contains the string representations of the Fish in the Aquarium’s internal list, in the same order that they appear in that list. Insert tab ("nt") and newline ("nn") characters to ensure that, when this string is displayed, no more than two Fish are printed per line (if there are an odd number of fish, the last one will be printed on a line by itself). For example, a call to this method might return a string like




"<< (Bill, red Gourami)nt<< (Ted, yellow Goldfish)nn<< (Mary, pink Mollie)". Note that you can call str() on a Fish (or any other object) to automatically invoke its __repr__() method.







CSE 101 – Lab #8 Page 2
add(self, newFish)




If the number of Fish in the Aquarium is less than its capacity, this method appends its argument to the list of Fish and returns True. Otherwise, it returns False without modifying the list.




population(self)




This method returns the number of Fish that are currently held in the Aquarium.




countType(self, type)




This method returns the number of Fish in the Aquarium whose species matches the type parameter. For example, myTank.countType("Guppy") would return the number of Fish in myTank that have “Guppy” as their species.







 
Finally, complete the fillAquarium() function. This function takes two arguments: a string representing the name of a (plain text) data file, and a positive (non-zero) integer representing the tank capacity in gallons. It returns a new Aquarium object. fillAquarium() does the following:




 
It creates a new Aquarium with the specified capacity.




 
It uses a loop to open the specified data file. For each line in the data file:




The function calls createFish() with the current line to get a new Fish. The function attempts to add the new Fish to the Aquarium object.




 
It returns the new Aquarium.







Sample Output




When you have completed the assignment, your program should produce output similar to the following using the supplied sample data files:







Creating three new fish...




Fish 1: << (Homer, red Guppy)




Fish 1 is a Guppy




Fish 2: << (Marge, blue Cichlid)




Fish 2 is a Cichlid




Fish 3: << (Bart, yellow Tetra)




Fish 3 is a Tetra




Fish 1 is larger than Fish 2




Fish 1 is larger than Fish 3




The test tank’s current population is: 0




Adding fish now...




The test tank’s new population is: 3




<< (Homer, red Guppy) << (Marge, blue Cichlid)




<< (Bart, yellow Tetra)




The test tank contains 1
Cichlid(s).
The test tank contains 1
Guppy (or Guppies).
The test
tank
contains
1
Tetra(s).
The test
tank
contains
0
Mollie(s).












CSE 101 – Lab #8 Page 3
Creating a new 15-gallon aquarium from tank1.txt...




tank1 contains 12 fish:




<< (Alvin, orange Tetra) << (Simon, gray Guppy)




<< (Theodore, blue Oscar) << (Bart, yellow Cichlid)




<< (Lisa, green Barb) << (Homer, yellow Goldfish)




<< (Marge, red Gourami) << (Maggie, pink Mollie)




<< (Ned, gray Cichlid) << (Maude, orange Barb)




<< (Krusty, white Gourami) << (Bob, green Cichlid)




Creating a new 30-gallon aquarium from tank2.txt...




tank2 contains 20 fish:




<< (Zippy, yellow Barb) << (Sparky, green Goldfish)




<< (Itchy, white Barb) << (Scratchy, black Cichlid)




<< (Manny, green Mollie) << (Moe, yellow Gourami)




<< (Jack, white Gourami) << (Dexter, blue Goldfish)




<< (Rob, black Gourami) << (Eddie, yellow Tetra)




<< (Jesse, gray Mollie) << (Dave, gray Cichlid)




<< (Danny, yellow Guppy) << (Billy, yellow Gourami)




<< (Mary, gray Mollie) << (Sue, red Oscar)




<< (Barbara, yellow Mollie) << (Dinah, orange Oscar)




<< (Ellen, gray Oscar) << (Joan, yellow Guppy)




Creating a new 10-gallon aquarium from tank3.txt...




tank3 contains 10 fish:




<< (Mario, black Tetra) << (Luigi, white Mollie)




<< (Peach, orange Guppy) << (Toad, red Guppy)




<< (Bowser, yellow Mollie) << (Koopa, black Barb)




<< (Link, black Gourami) << (Zelda, green Mollie)




<< (Luke, orange Cichlid) << (Leia, red Tetra)





















































































CSE 101 – Lab #8 Page 4