CCircle.Lab.3 : Python Lists, Functions and Objects

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Welcome to Lab 3

For questions asking you to figure out what is printed when certain code is evaluated, please write down your solution to the problem before trying to run the provided code on your computer.

Lists

  1. Complete the function below with a single line of code. 
     def squared_list(list_of_integers):
 """Returns a list corresponding to the input list of integers, with all elements squared.

 >>> squared_list([1, 2, 3])
 [1, 4, 9]
 """
 return _________________________
  2. Complete the function below. 
     def square_elements(list_of_integers):
 """Mutates the input list of integers, squaring all elements.

 >>> ints = [1, 2, 3]
 >>> square_elements(ints)
 >>> ints
 [1, 4, 9]
 """

     __________________________

     __________________________

     __________________________
  3. Complete the function below. 
     def reverse(a_list):
 """Mutates the input list, reversing the elements.

 >>> ints = [1, 2, 3]
 >>> reverse(ints)
 >>> ints
 [3, 2, 1]
 """

     __________________________

     __________________________

     __________________________

    Extra for Experts

  4. There is a built-in function zip, which takes two lists and ‘zips’ them together. An example is 
     >>> for tuple in zip([1, 2], ['a', 'b']):
 ...    print tuple
 (1, 'a')
 (2, 'b')

    The documentation for zip is

     zip(...)
     zip(seq1 [, seq2 [...]]) -> [(seq1[0], seq2[0] ...), (...)]

 Return a list of tuples, where each tuple contains the i-th element
 from each of the argument sequences.  The returned list is truncated
 in length to the length of the shortest argument sequence.

    Write function my_zip that mimics the behavior of zip.

         def my_zip(a, b):

         __________________________

         __________________________

         __________________________

         __________________________

         __________________________

         __________________________

         __________________________

         __________________________

Functions

  1. Fill in the blanks in the following function definition for adding a to the absolute value of b, without calling abs. 
     from operator import add, sub

 def a_plus_positive_b(a, b):
     """Returns the sum of a and the positive value of b, without calling the abs() built-in.

     >>> a_plus_abs_b(3, 4)
     7
     >>> a_plus_abs_b(3, -4)
     7
     """

     if b < 0:
         f = _____
     else:
         f = _____
     return f(a, b)
  2. Write what is printed when the following code is evaluated. 
     def boom():
     return 1 / 0

 boom
 boom()
  3. Write what is printed when the following code is evaluated. 
     def hmm(a=[]):
   a.append(1)
   return a

 print(hmm())
 print(hmm())
 print(hmm())
  4. Write what is printed when the following code is evaluated. 
     def magic_print(a, b):
   print(print(a), print(b))

 magic_print(1, 2)

    Extras for Experts

  5. Write what is printed when the following code is evaluated. 
     from operator import add, mul

 def f(x, y):
     print('batman ', y)
     return add(add(x, y), 1)

 def g(x, y):
     print('robin ', x)
     return mul(mul(x, y), 2)

 f(2, g(2, f(500, 2)))
  6. These steps give the hailstore sequence, as written in Douglas Hofstadter’s book Gödel, Escher, Bach. 
     Pick a positive integer n as the start.
 If n is even, divide it by 2.
 If n is odd, multiply it by 3 and add 1.
 Continue this process until n is 1.

    Write function hailstone(n) to print the hailstone sequence starting at n, and return its length.

     def hailstone(n):

     __________________________

     __________________________

     __________________________

     __________________________

     __________________________

     __________________________

     __________________________

     __________________________

     __________________________

     __________________________

     __________________________

Objects

  1. Write what is printed when the following code is evaluated. 
     class Song(object):

     def __init__(self, lyrics):
         self.lyrics = lyrics

     def print_song(self):
         for line in self.lyrics:
             print line

 roses_song = Song([
     "Roses are red"
     , "Violets are blue"
     , "Carnations can also be red..."
     , "Woohoo!"
 ])

 roses_song.print_song()

    Extra for Experts

  2. Write what is printed when the following code is evaluated. 
     o = min
 o = max
 g, h = (min, max)
 max = g
 goo = max(o(3, g(2, h(1, 5), 3)), 4)

 print(goo)

Congratulations

You’ve completed this lab!

Next -> Lab 4: Python Dictionaries