Lecture 19 - Exercises

19A - Mutable Objects and Functions

I recommend drawing the memory diagram as you execute each of the following programs.

1. What does the following program print?

   def z0(y):
       y[0] = 4
       return y
   
   b = [5, 6]
   c = z0(b)
   print(b[0], c[0])

2. What does the following program print?

   def z4(d1, d2):
       a = d1
       d1 = {}
       d1 = d2
       d1["A"] = 2
       return a
   
   a = {"A": 4, "B": 6}
   b = {"A": 6, "B": 11}
   f = z4(a, b)
   print(a["A"], b["A"], f["A"])

Problems

1. Implement the following function, without using any built-in list methods:

   def find(v, lst):
       """ Return the index of the first occurrence of v in lst. 
       Return -1 if v is not in the list. Precondition: lst is a list. """

2. Implement the following function:

   def remove_all(v, lst):
       """ Remove all occurrences of v from lst. Precondition: lst is a list. """

3. Implement the following function:

   def without(v, lst):
       """ Return a new list that contains all elements in lst except those equal to v.
           Precondition: lst is a list. """

4. Implement the following function, without using any built-in list methods, in such a way that you index into the list less than len(sorted_lst) times.

   def find(v, sorted_lst):
       """ Return the index of the first occurrence of v in lst.  Return
       -1 if v is not in the list. Precondition: lst is a list of things that
       can be compared with the < operator, and is in sorted order 
       (i.e. lst[i] <= lst[i+1] for    all i in range(len(lst)-1) """