Key Ideas

  • A list is an ordered collection of items that can be of any type, e.g. ["Computer Science", 2017, 3.1415, False].
  • List creation
    • boys = ["Brady", "Jacob", "Quinn", "Tjabe", "Luke"]
    • girls = ["Aubrey", "Sarah", "Anya", "Maggie", "Eliana", "Addy"]
    • students = [boys, girls]
  • Determining List Length: len
  • Accessing List Elements
    • boys[1]
    • students[1][2]
  • List Membership: in and not in
  • List Concatenation: +
  • List Repetition: *
  • List Slices
    • girls[2:4]
    • girls[:2]
    • girls[2:]
  • Lists are mutable (unlike Strings)
    • Replacement: boys[0] = "Seamus"
    • Deletion: boys[1:3] = []
    • Deletion: del(boys[0])
  • List Aliasing: students = boys
  • List Cloning: students = boys[:]

Averages Problem

Write a function called average that takes a list of numbers as a parameter and returns the average of the numbers.

def average(numbers):
    total = 0
    for number in numbers:
        total += number

    return total / len(numbers)

def average_2(numbers):
  return sum(numbers) / len(numbers)  # a much simpler (and more elegant) solution using the built-in sum() function

numbers = [1, 2, 3, 4, 5]
print(average(numbers))

Max Number Problem

Write a Python function named max that takes a parameter containing a nonempty list of integers and returns the maximum value. (Note: there is a built-in function named max() but pretend you cannot use it.)

def max_num(numbers):
    biggest = 0
    for item in numbers:
        if item > biggest:
            biggest = item

    return biggest

def max_num2(numbers):
  return max(numbers)   # the illegal (but more elegant) solution using built-in max() function    

numbers = [54, 23, 84, 57, 23, 90]
print(max_num(numbers))

HW:

Use the following code to answer the questions below:

boys = ["Brady", "Jacob", "Quinn", "Tjabe", "Luke"]
girls = ["Aubrey", "Sarah", "Anya", "Maggie", "Eliana", "Addy"]
students = [boys, girls]
  1. What output would the following commands create?
    • print(boys[2])
    • print(girls[3:])
    • print(students[0][0])
    • print(students[1][1:4])
  2. Explain the difference between these two commands:
    • students = boys
    • students = boys[:]
  3. What command could we use to add another boy, named “Seamus”, to the boys list?