1
h03
CCS CS20 S18
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h03: Perkovic 2.4-2.5 (Objects, Classes, types, libraries)

ready? assigned due points
true Tue 04/17 12:30PM Sat 04/21 12:00PM

You may collaborate on this homework with AT MOST one person, an optional "homework buddy".

This assignment should be submitted by scanning the pages in the correct order to a PDF file and uploading to gradescope.com.

For more information, visit ucsb-cs8.github.io and look for Gradescope: Student Self Submission under "topics".

Even though it is a Gradescope submission, nevertheless, *please fill in the information at the top of this homework sheet*, including your name and umail address.

READING ASSIGNMENT

Please read Perkovic 2.4-2.5 (Objects, Classes, types, libraries). Then complete these problems.

  1. (10 pts) These 10 points are for filling in your name at the top of the sheet, and scanning correctly on Gradescope. (Having these here gives me a place to give you feedback if there is some glitch with the way you are doing it.)

  2. As discussed in Section 2.4, the type() function returns the type of a Python value. When you pass a variable such as x, type(x) returns the type of the value that the variable x currently refers to.

    Assume that the following assignment statement has been executed:

    schools=["UCSB","Stanford","UCSD","Cal Poly"]

    What will each of the expressions below evaluate to? As a reminder, strictly speaking, Python will print types in the format <class 'int'>, <class 'float'>, <class 'str'>, etc. so please use exactly that format for full credit.

    Points Expression Result Points Expression Result
    (4 pts) type(3)   (4 pts) type(1+2.5)  
    (4 pts) type('3')   (4 pts) type(2 * "3")  
    (4 pts) type("3.5")   (4 pts) type((3,3))  
    (4 pts) type(3.5)   (4 pts) type(schools)  
    (4 pts) type([3,5])   (4 pts) type(schools[0])  

  3. (10 pts) Assume that cases is the name of a variable with a float value that you want to convert to an integer value. Write a Python expression that converts cases to an integer (throwing away any fractional part)

  4. (10 pts) Assume that courseNum is an integer that represents the numeric part of a course number (e.g. 3, 8, 130, 16, 24). Write a Python expression that converts courseNum to an string (i.e. <class 'str'> in Python)

  5. (10 pts) If you want to check whether x is greater than 10, and y is greater than 5, you can write the Python expression

    (x > 10) and (y > 5)

    If x has the value 20, and y has the value 17, this evaluates to True.

    But what if we accidentally wrote it as:

    (x > 10) + (y > 5)

    What would this expression evaluate to, assuming the same values for x and y)? (The answer requires you to read the section carefully, and then apply what you have learned. I suggest you try that first before trying it at the Python command line.)

  6. Both Sections 2.4 and 2.5 mention a type of function that is called a constructor.

    1. (5 pts) In general, what do constructors do? (Don’t give an answer that is specific, for instance, to only the constructor for the int data type).

    2. (5 pts) Before using the constructor for a Fraction object, a particular line of Python code must be written. What is that line of code? (Be very careful about spelling and upper vs. lower case.)

    3. (10 pts) Assuming that line of code has been typed (the one mentioned in the previous question), how do you create a Fraction object that holds the fraction (i.e., “four fifths”), and makes the variable ratio refer to that object?