Peer Instruction: Tuples Multiple Choice Questions¶

11-9-1: In what situation does the below code fail?

def find(lst, value):
   '''(list, value) -> int
   Return the first occurrence of value in lst.
   If value is not found, return -1.
   >>> find([20, 40, 60], 40)
   1
   '''
   i = 0
   num = lst[i]
   while num != value:
      i = i + 1
      num = lst[i]
   if i < len(lst):
      return i
   else: return -1

It never fails
Incorrect! Because 'num = lst[i]' goes out of range when the list is empty or the value is not found in the list
It fails when the list is empty
Incorrect! Because 'num = lst[i]' goes out of range when the list is empty or the value is not found in the list
It fails when the value is not found in the list
Incorrect! Because 'num = lst[i]' goes out of range when the list is empty or the value is not found in the list
Both B and C will fail
Correct! Because 'num = lst[i]' goes out of range when the list is empty or the value is not found in the list

11-9-2: To represent groups of students, we can use a nested list. For example, in the following list, students 1, 3, and 4 are together in a group, and student 2 is working alone: [[1, 3, 4], [2]]. In the following code, which call would return True?

def is_ok(group_list, class_list):
   '''(list of list of int, list of int) -> bool
   Return True iff every student in class_list is in exactly
   one group according to group_list.
   '''

is_ok([[1, 2], [2, 3]], [1, 2, 3])
Incorrect! Because 2 is in two different groups- [1, 2] and [2, 3]
is_ok([[1, 2], [4]], [1, 2, 3])
Incorrect! Because 3 is not in the group_list and 4 is not the class_list
is_ok([], [1, 2, 3])
Incorrect! Because there's no group list at all
is_ok([[1, 2], [4]], [1, 2, 3, 4])
Incorrect! Because 3 has not be assigned to any group
None will return True
Correct! Because there's no option where the group list has assigned every student to exactly one group