CIT 591 Midterm

Name ________________________________________

(5 points) Write a function letter_count to count the number of letters in a string, returning the result as an integer. You may wish to use the isalpha method for characters. Part of the function has been provided for you.
def letter_count(s): count = 0

return count
(5 points) Write a function extremes that, given a nonempty list of integers, returns the pair (least, greatest), where least is the smallest number in the list, and greatest is the largest number in the list. You may use Python's built-in functions in your function definition.

def extremes(lst):

(5 points) Give an English description of what the following function does.

import random
def points(n):
    directory = {}
    for i in range(0, n):
        pname = chr(ord('a') + i)
        x = 1000.0 * random.random()
        y = 1000.0 * random.random()
        directory[pname] = (x, y)
    return directory

(15 points) Each of the following pieces of code has an error. Tell what the error is and how to correct it.
1. # nums is a list of integers. Add the first and last numbers in the list, # and append the result to the list. nums = nums.append(nums[0] + nums[-1])
2. # Delete negative numbers from the list for i in lst: if lst[i] < 0: lst.remove(lst[i])
3. # print the average of the three given numbers a, b, c print "The average is " + (a + b + c) / 3

(5 points) Given the following function:

def foo(s):
    d = {}
    for ch in s:
        v = d.get(ch, 0)
        d[ch] = v + 1
    return d

what is returned by the call foo("sassafras") ?

(5 points) Given the following function:

def letters(s):
    ss = []
    for ch in s:
        if ch.isalpha():
            ss.append(ch.lower())
    return ss

what is returned by the call letters("1 and 2 and 3") ?

(5 points) Given the following function:
```
def lets(s):
    return "".join(filter(lambda x: x.isalpha(), list(s)))
```
what is returned by the call lets("1 and 2 and 3") ?
(5 points) Given the following function:
```
def f(n):
    return [foo, points, letters, lets][n]
```
what is returned by the call f(1) ?
(10 points) Suppose you are defining a class Circle, and every object of this class must have three values: The x and the y coordinates of the circle's center, and the radius of the circle.
1. Write the constructor that you would put in this class.
2. Use the above constructor to create a circle named unitCircle with radius = 1 and center at the origin (x = y = 0).
(5 points) What is the purpose of the following code in a Python program?
```
 if __name__ == '__main__':
    main()
```
(5 points) Use a list comprehension to assign to the variable oddCubes the cubes of the odd integers between 0 and100.
(15 points) Assume that you have written a class ListUtils to provide a number of operations on lists. This class is in the file listutils.py. In the following three questions you will write a complete class to test one of the functions in ListUtils.
1. Write the necessary import statements and the class header for a class named ListUtilsTest.
2. Write a test for the function duplicate(lst) which is supposed to return a shallow copy of the list given as a parameter.
3. Write the statement or statements necessary to perform the tests in the ListUtilsTest class.

(5 points) Given the function

def fiddle(index, lst):
    index += 1
    lst[index] += 1

what will be printed by

n, nums = 3, range(1, 6)
fiddle(n, nums)
print n, nums

(5 points) In IDLE, what is the value of the variable _ (a single underscore)?
(5 points) Give one way in which using TDD, Test Driven Design, may improve the style (not the correctness) of a program.