Sample Final

  1. Evaluate each expression. Indicate floats by including a decimal point (so to show 1 as a float, write “1.0”) If any cannot be evaluated, say why.
    1. 3 + 5.0
    2. 10 % 4 + 7 / 2
    3. abs(5 - 20 / 3) ** 4
    4. range(4, 13, 3)
    5. "If %d + %d = %2.2f, then %s" % (2, 2, 4, "bye!")
    6. 4 / "3"
    Answer:
    1. 8.0
    2. 5
    3. 1
    4. [4, 7, 10]
    5. "If 2 + 2 = 4.00, then bye!"
    6. A string cannot divide an integer, so this produces a TypeError
  2. Convert the following into Python:
    1. The volume vol of a sphere is 4πr divided by 3 (remember the result is a floating point number!).
    2. The value of the string variable str with all occurrences of the letter “e” replaced by the character “3”
    3. Subtract 159 from the product of 3 and 27, using integers
    Answer:
    1. include math
      vol = 4.0 * math.pi * r / 3.0
    2. include string
      string.replace('e', '3')
    3. 3 * 27 - 159
  3. The A–F grading system assigns the following grades to scores. If your score is less than 1 point, you get an F; if it is less than 2 points, you get a D; if it is less than 3 points, you get a C; if you get less than 4 points, you get a B; and if you get 4 points or more, you get an A. Write an “if” statement that, given a score in the variable score, prints the corresponding grade.
    Answer:
    if score < 1:
        print "F"
    elif score < 2:
        print "D"
    elif score < 3:
        print "C"
    elif score < 4:
        print "B"
    else:
        print "A"
  4. What does the following function do when given a list of numbers as the argument?
    def f(lst):
        a = i = 0
        n = len(lst)
        while i < n:
            if lst[i] <= 0:
                i += 1
                continue
            a += lst[i]
            i += 1
        return float(a) / n
    Answer: This computes the (floating point) average of the positive numbers in the list lst.
  5. Rewrite the function in problem 4 so that it uses a “for” loop, not a “while” loop.
    Answer:
    def f(lst):
        a = 0
        for i in lst:
            if i <= 0:
                continue
            a += i
        return float(a) / len(lst)
  6. What does the following program do:
    d = dict()
    while True:
        try:
            line = raw_input("EOF to stop> ")
        except EOFError:
            break
        for i in line:
            d[i] = d.get(i, 0) + 1
    u = d.keys()
    for i in u:
        print i, d[i]
    Answer: This prints a list of characters in the input (excluding the newlines and/or carriage return), and the number of times each character appears in the input.
  7. What does the following program do:
    def y(n):
        if n < 10:
            return str(n)
        else:
            d = str(n % 10)
        return y(n / 10) + d
     
    print y(174)
    Answer: The function prints the digits in the number n. So, this prints
    174