Chapter 8: Lists Keep Things In Order

The answers on this page show ONE way to solve the exercises. However, there are usually OTHER ways to accomplish the same thing. This is OK!

A suggested solution is ONE way to solve the problem, not the ONLY way.

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Solutions

Part One: Adding and Removing Items

1. Create a list called adding_practice with a single entry: 273.15. Use the append method to add the following elements to the list one at a time. Print the list after each step to confirm the changes.

   # Create a new list with one entry.
   adding_practice = [273.15]
   print(adding_practice)
   
   #b. Append new element 'hello' to the list:
   adding_practice.append('hello')
   print(adding_practice)
   

2. Use concatenation to add these three items to the list all at once: [False, -4.6, '87'].

   adding_practice += [False, -4.6, '87']
   

3. append, insert, pop, and remove are used to add or remove elements from a list. Bracket notation can be used to modify any element within a list. Starting with the cargo_hold list write statements to do the following:

   #We can split lists across lines! This makes longer lists easier to read.
   cargo_hold = ['oxygen tanks', 'space suits', 'parrot', 'instruction manual',
       'meal packs', 'slinky', 'security blanket']
   
   #a. Use bracket notation to replace 'slinky' in the list with 'space
   tether'.
   cargo_hold[5] = 'space tether'
   print(cargo_hold)
   
   #b. Remove the last item from the list with pop. Print the element removed and the updated list.
   
   removed = cargo_hold.pop()
   print('\nb) Element removed:', removed)
   print('Cargo hold:', cargo_hold)
   
   #d. append and insert require arguments inside the ().
   # Add the items 1138 and '20 meters' to the list.
   # the number at the start and the string at the end.
   # Insert 1138 at index 0.
   cargo_hold.insert(0, 1138)
   cargo_hold.append('20 meters')
   print('\nd) Cargo hold:', cargo_hold)
   
   #e. # Use the remove method to take the parrot out of cargo_hold.
   cargo_hold.remove('parrot')
   print('\ne) Cargo hold:', cargo_hold)
   
   #f. Use .format() to print the final list and its length.
   # "The list ___ contains ___ items."
   output = "The list {0} contains {1} items."
   print('\nf)', output.format(cargo_hold, len(cargo_hold)))
   

Back to the exercises.

Part Two: Slices & Methods

1. Using the slice syntax list_name[start : end] you can either insert, replace, or remove items from a list.

   Use slices to make the following changes to the final cargo_hold list from part 1. Be sure to print the list after each step to confirm your work.

   cargo_hold = [1138, 'space suits', 'parrot', 'instruction manual', 'meal packs',
    'space tether', '20 meters']
   
   # Use SLICES to make the following changes to the cargo_hold list.
   
   #a. Insert the string 'keys' at index 3 without replacing any other entries.
   cargo_hold[3:3] = ['keys']
   print(cargo_hold)
   
   #b.  Remove 'instruction manual' from the list.
   index = cargo_hold.index('instruction manual')
   cargo_hold[index:index+1] = []
   
   #c Replace the elements at indexes 2-4 with the items 'cat', 'book', and 'string cheese'.
   # Remember that slices go from the start index up to but NOT including the end index.
   cargo_hold[2:5] = ['cat', 'book', 'string cheese']
   

2. Some methods—like append and pop—alter the original list, while others do not. Use the lists

   supplies_1 = ['duct tape', 'gum', 3.14, False, 6.022e23]
   supplies_2 = ['orange drink', 'nerf toys', 'camera', '42', 'Rutabaga']
   

   to see if taking a slice or using the reverse and sort methods changes the original list.

   #a. Print a slice of the last 3 items from supplies_1.
   print('Slice:', supplies_1[-3:])
   print('After slice:', supplies_1)
   
   # Does slice alter the original list?
   #Conclusion: Taking a slice does NOT alter the original list!
   
   #b. reverse the first list, sort the second, and then print both lists.
   supplies_1.reverse()
   supplies_2.sort()
   print('Reversed:', supplies_1)
   print('Sorted:', supplies_2)
   
   #c. Do reverse or sort alter the original lists? Both alter the original list.
   

Back to the exercises.

Part Three: Split, List, and Join

1. The split method converts a string into a list, while the join method does the opposite.

   #a. Print phrase.split() vs. phrase.split('e') vs. list(phrase).
   phrase = 'In space, no one can hear you code.'
   
   print(phrase.split())
   print(phrase.split('e'))
   print(list(phrase))
   
   # What is the purpose of the argument inside the ()?
   #The argument inside .split() identifies where to divide in the string.
   
   #b. print ''.join(my_list) vs. 'a'.join(my_list) vs.'_'.join(my_list).
   my_list = ['B', 'n', 'n', '5']
   print(''.join(my_list))
   print('a'.join(my_list))
   print('_'.join(my_list))
   
   # What is the purpose of the argument inside the ()?
   #The argument inside .join() is the list of elements to attach together in a new string.
   
   #d. Do split, list, or join change the original string/list?
   #.split(), .join(), and list() do NOT change the original string/list.
   

Back to the exercises.

Part Four: Multi-dimensional Lists

1. Lists can hold different data types, even other lists! A multi-dimensional list is one with entries that are also lists.

   #a. Define and assign the following lists, which hold the name, chemical
   symbol and mass for different elements:
   
   # Here are three, 'one-dimensional' lists:
   element_1 = ['hydrogen', 'H', 1.008]
   element_2 = ['helium', 'He', 4.003]
   element_26 = ['iron', 'Fe', 55.85]
   
   #b. Append each of the element lists to 'table'.
   #'table' is a 2-dimensional list. Each element in table is also a list!
   table = []
   table.append(element_1)
   table.append(element_2)
   table.append(element_26)
   print(table)
   print(len(table))
   
   #c. Examine the difference between printing table[1] and table[1][1].
   #Explain the difference between the first and second index in table[1][1]
   #The first [] returns the index element list in table (element_2).
   #The second [] return the index value within the first[] element list (he)
   
   #d. Print symbol from element_26.
   print(table[2][1]))
   

2. OPTIONAL: table is an example of a 2-dimensional list. The first “level” contains the element lists, and the second level holds the name/symbol/mass values.

   Now create a 3-dimensional list. A good mental model is to think of a filing cabinet.

   #a. Define at least four, 1-dimensional lists. Call each one a *folder*.
   folder_1 = ['page_1', 'page_2', 'page_3']
   folder_2 = ['page_9', 'page_8']
   folder_3 = ['page_a', 'page_b', 'page_c']
   folder_4 = ['page_x', 'page_y', 'page_z']
   
   #b. Now define at least two, 2-dimensional lists. Call these lists *drawers*.
   #Each element in the list is one of the folders.
   drawer_1 = [folder_1, folder_2]
   drawer_2 = [folder_3, folder_4]
   
   #c. Now define one 3-dimensional *cabinet* list.
   #Each element is one of the 2-D drawer lists.
   cabinet = [drawer_1, drawer_2]
   

Back to the exercises.