16.8: Chapter 9

9.1 Modifying and iterating lists

1. b. The append() operation adds an element to the end of a list.

2. c. The element to be removed is passed as a parameter to the remove operation. The remove is performed on the specified list.

3. c. Both pop() and remove() can be used to remove the last element of a list. pop() automatically removes the last element, whereas remove() requires the last element be specified.

4. a. The length of the list is 5, so the iterative for loop executes five times.

5. b. len(my_list) is 5. A counting for loop ends at 1 less than the second value in the range function, so the final value of i is 4 .

6. a. The for loop steps by two each time, so index 0, 2, and 4 are printed. Due to the "end=" in the print statement, all elements are printed on one line.

9.2 Sorting and reversing lists

1. b. Sorting in descending order means to arrange the elements from largest to smallest. -3 is the smallest element of the list and would be the last element when the list is sorted in descending order.

2. a. For strings, ascending order refers to dictionary order.

3. c. In alphabetical order, "h" comes before "k". The first four characters are the same, so "flash" comes before "flask" .

4. b. The sort() function must be applied on the list. The default for the sort() function is to arrange elements in ascending order.

5. a. The correct syntax for the reverse() function requires the function to be applied to the list.

6. a. "go" is the first element of board_games, so "go" would be the last element once board_games is reversed.

9.3 Common list operations

1. a. The min() function takes a list as a parameter and returns the minimum for the list.

2. b. "Austin City Limits" is the first string in dictionary order.

3. c. The summation of the given floats is 12.4 .

4. c. list2 refers to the same list as my_list, so any changes made to list2 also reflect on my_list. 18 is the summation of the values in the list.

5. a. 3 is the maximum value in the list my_list. Line 3 changes the value of the first element in list2.

6. b. sum() function is not defined for string values.

9.4 Nested lists

1. a. Each row of the matrix is represented as a list in the larger list-of-lists, matA. matA represents the complete matrix.

2. c. 6 is in the 2nd row and 3rd column. Using zero-indexing results in index 1 for the row and 2 for the column.

3. c. The first element of the list matA is a list [7, 4, 5] representing the first row of the matrix.

4. a. The outer for loop iterates row by row. The inner for loop iterates through each element in a row. So all the numbers are printed, starting from 7 and ending in -5.

5. c. The outer for loop runs for three iterations because there are three elements in the list-of-lists. The inner for loop iterates through each element of each row using the length of each row.

9.5 List comprehensions

1. a. The expression tells Python what element to put in the new list.

2. c. i+2 results in adding 2 to each element of a_list to generate b_list.

3. b. The for loop starts at 1 and steps by three, so it begins at 1 and ends at 13. Dividing using the // operator results in dropping the part after the decimal.

4. c. The list comprehension filters for negative numbers in my_list.

5. b. The list comprehension selects vowels from the given string.

6. a. The for loop ranges from 0 through 20, stepping by two, but each iterated element is even, so nothing is added to new_list.