Exercise Solutions: Lists

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.

    1. 42
    adding_practice.append(42)
    

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  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

    ['oxygen tanks', 'space suits', 'parrot', 'instruction manual', 'meal packs', 'slinky', 'security blanket']
    

    write statements to do the following:

    1. Use bracket notation to replace 'slinky' in the list with 'space tether'. Print the list to confirm the change.

      cargo_hold[5] = 'space tether'
      
    2. Remove the last item from the list with pop. Print the element removed and the updated list.

    3. Remove the first item from the list with pop. Print the element removed and the updated list.

    4. append and insert require arguments inside the (). Add the items 1138 and '20 meters' to the the list—the number at the start and the string at the end. Print the updated list to confirm the changes.

      cargo_hold.append('20 meters')
      cargo_hold.insert(0, 1138)
      
    5. remove the parrot from the cargo hold, then print the updated list.

    6. Use format() to print the final contents of the list and its length. "The list ___ contains ___ items."

      output = "The list {0} contains {1} items."
      print(output.format(cargo_hold, len(cargo_hold)))
      

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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.

    1. Insert the string 'keys' at index 3 without replacing any other entries.
    2. Remove 'instruction manual' from the list. (Hint: The index method is helpful to avoid manually counting an index).
    3. Replace the elements at indexes 2 - 4 with the items 'cat', 'book', and 'string cheese'.
    cargo_hold[2:5] = ['cat', 'book', 'string cheese']
    

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  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.

    1. Print a slice of the last 3 items from supplies_1. Does slice alter the original list? Verify this by printing supplies_1 after taking the slice.

      print('Before slice:', supplies_1)
      print('Slice:', supplies_1[-3:])
      print('After slice:', supplies_1)
      print("Conclusion: Taking a slice does NOT alter the original list!")
      
    2. reverse the first list, sort the second, and then print both lists. What is the difference between the two methods?

    3. Do reverse or sort alter the original lists?

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Part Three: Split, List, and Join

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

    1. Try it! Given the string phrase = 'In space, no one can hear you code.', see what happens when you print phrase.split() vs. phrase.split('e') vs. list(phrase). What is the purpose of the argument inside the ()?

      output = "Using {0}: {1}"
      print(output.format('.split()', phrase.split()))
      print(output.format(".split('e')", phrase.split('e')))
      print(output.format('list()', list(phrase)))
      
    2. Given the list my_list = ['B', 'n', 'n', 5], see what happens when you print ''.join(my_list) vs. 'a'.join(my_list) vs. '_'.join(my_list). What is the purpose of the argument inside the ()?

    3. We can take a string with delimiters (like commas) and convert it into a modifiable list. Try it! Split the string 'water,space suits,food,plasma sword,batteries' at each comma, alphabetize the list with sort, then combine the elements into a new string. Use a hyphen to join the elements together in the string.

      items = cargo_hold.split(',')
      items.sort()
      new_string = '-'.join(items)
      print(new_string)
      
    4. Do split, list, or join change the original string/list?

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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.

    1. Define and assign the following lists, which hold the name, chemical symbol and mass for different elements:

      1. element_1 = ['hydrogen', 'H', 1.008]
      2. element_2 = ['helium', 'He', 4.003]
      3. element_26 = ['iron', 'Fe', 55.85]
    2. Define the list table, and use table.append(list_name) to add each of the element lists to it. Print table to see its structure.

      table = []
      table.append(element_1)
      table.append(element_2)
      table.append(element_26)
      

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    3. Use bracket notation to examine the difference between printing table[1] and table[1][1]. Don’t just nod your head! I want to HEAR you describe this difference. Go ahead, talk to your screen.

    1. Using bracket notation and the table list, print the mass from element_1, the name from element_2 and the symbol from element_26.

      output = "To get the {0} from {1}, the syntax is {2}. Result = {3}."
      print(output.format('mass', 'element_1', 'table[0][2]', table[0][2]))
      

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    2. 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.

    3. Optional: Create a 3-dimensional list and print out one entry from each level in the list.

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