Arrays and Lists

Fred Agbo

October 14, 2026

Happy Wednesday

Quick Announcements

  • Midterm exam 1 review/solution is posted on Canvas
  • Project Breakout is due next week Monday
  • Starting early is a key factor to success
  • Attend your session meeting for more help and tools needed to succeed on the Breakout project.

Midterm Polling

  • If there’s a single most important thing to do to help you improve in content understanding and grades in this class what would that be?

    • Being allowed to work on a project over an extended period
      • Unfortunately, this is how the curriculum has been built for years!
        • Intensive!
    • Take time in class to go over the homework before it’s due.
      • I strongly recommend to start working on homework from Tuesdays
      • Visiting office hours and QUAD Center, and ask Section leaders
    • Videos and its grade points; Spend some class time talking about the video concepts
      • Please consistently watch the videos. The points are huge overtime.
      • I have and will continue to reinforce the topic in the video before jumping to the activities.
    • Further explaining what certain lines of code do.
      • Raise your hand to ask me questions or to repeat my explanation.
    • I wasn’t as understanding of the material as I could be …
      • Read the text material shared with you chapter by chapter.
      • This is a useful supplementary material upon which ALL the lecture contents in the class was built.

Arrays and Lists

  • From the earliest days, programming languages have supported the idea of an array, or an ordered sequence of values.
  • Individual values in an array are called elements, and the number of elements is the length of the array.
  • Each element’s position in the array is given by its index, with index numbers starting at 0 and extending up to 1 less than the length of the array
  • Python implements the array concept in a bit more general form called a list.

Reminder: Making Lists

  • Created using square brackets with elements separated by commas:

    COIN_VALUES = [1, 5, 10, 25, 50, 100]
COIN_NAMES = [ "penny", "nickle", "dime",
               "quarter", "half-dollar", "dollar" ]

  • Lists are commonly represented visually or conceptually as a series of numbered boxes:

What we already know

  • Can retrieve the value of any element in a list by writing the index of that element in square brackets after the list name

    • COIN_VALUES[3] ⟶ 25
    • COIN_NAMES[2] ⟶ "dime"

  • Can concatenate two lists to form a new list with elements from both

    • [1,2,3] + [4,5,6]⟶ [1,2,3,4,5,6]

  • Can loop through each of the list elements in turn

    for elem in my_list:
  # do stuff with elem

    where elem is the name of the variable that will sequentially get assigned the value of every element in my_list

Sequences

  • Sound familiar? Lists are just like more general strings!
  • Strings and lists are examples of a more general class of object in Python called sequences
  • We already knew that all sequences support:
    • The len function
    • Index numbering starting at 0
    • Concatenation using + or +=
    • Selection of an individual element using square brackets
    • Looping over elements
  • We can now add:
    • Negative index numbering counting backwards from the end
    • Slicing in all forms
    • Comparing sequences
    • Repetition using *
    • Inclusion testing using in operator

Problem 1A: Tracing Understanding

What would the below expression evaluate to?

["One", 2, True][-1:1:-1][1]
  1. "n"
  2. 2
  3. True
  4. None of the above, or this will error

Problem 1B: Tracing Understanding

What would the below expression evaluate to? Or would it error out?

['One', 2, True][-1:1:-1][0]

Problem 2: Airline Boarding

  • This is a coding problem, work in pairs or trios on a single computer

  • In manifest.py, I’ve created a list of passenger information for an airline

  • The list has passenger information in a “name”, “age”, “seat” ordering

  • So, for example, the first few passengers look like:

    MANIFEST = [
  "Anthony Hutchinson", 77, "24A",
  "Carol Turner", 37, "8F",
  ...etc...
]

Problem 2b: Seat Taken?

  • In Prob2.py, you can add your code
  • Imagine a passenger would like to switch seats. It would be nice to have an easy function to check a potential seat assignment and determine if it is available
  • Complete the function is_seat_available to check to see if a particular seat is available (not currently assigned)
  • BONUS: Sometimes robots will ride the plane with names like ‘2F’. Make sure your function still would work properly in that case

Problem 2c: New Family

  • Switch who is typing!
  • A new family purchased tickets late! Add their information to the manifest.
    • Bill Yu, age 43, in seat 15C
    • Jackie Yu, age 39, in seat 15B
    • Hayden Yu, age 12, in seat 15A
  • Then, complete the function avg_age_window_seats, which returns the average age of all passengers riding in a window seat (“A” and “F” seats)
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