Lesson 11 Notes: Making a List, Checking it Twice

• What is a list?
  • A list is an ordered set of elements.
  • Lists are enclosed in [ ]
  • Each item in a list is separated by a comma
  • Examples:
    pets = ["dog", "cat", "bird", "elephant"]
nums = [1,2,3,4,5,6]
stuff = [1, 15, "gorilla", 23.9, "alphabet"]

• Lists inside of Lists
  • Lists may also contain other lists
  • A list inside a list is called a "nested list"
  • Example:
    to_do = ["clean up", ["feed dog", "feed cat", "feed fish"], "fix dinner"]
• Slicing Lists
  • Lists can be accessed just like strings by using the [ ] operators.
  • Example:
    list = ["Peter", "Andrew", "James", "John"]
print list [0]
>>> Peter
print list [1:]
>>> Andrew, James, John

• Accessing Nested Lists
  • To access an item in a nested list, provide two index addresses.
    word_list = ["dog", ["fluffy", "spot", "toto"], "mutt"]
print word_list [1] [1]
>>> "spot"

• Mutability
  • Unlike strings, lists are mutable, which means they can be changed.
  • Example:
    string = "dog"
string[0] = "f" # This is not a legal function
  • Example:
    list = ["d", "o", "g"]
list[0] = "f"
>>> ["f", "o", "g"]

• Dicing Lists
  • Lists can also be changed using the [ ] operators.
  • Example:
    list = ["Mark", "Luke", "John"]
list[0] = "Mattew"
print list
>>> "Matthew", "Luke", "John"

• Adding to Lists
  • To add items at the end of a list, use list.append("item")
  • Example:
    list = ["Matthew", "Mark", "Luke"]
list.append("John")
print list
>>>Matthew, Mark, Luke, John
• Deleting Items from Lists
  • Use del to remove item based on index position.
  • Example:
    list = ["Matthew", "Mark", "Luke", "John"]
del list[1]
print list
>>> Matthew, Luke, John

• Removing Item from List
  • To remove an item from a list without using the index position, use list_name.remove("item")
  • Example:
    kids = ["Bubba", "Sissy", "Froggy"]
kids.remove("Froggy")
print kids
>>> Bubba, Sissy

• What's in a list?
  • The keyword "in" can be used to test if an item is in a list.
  • Example:
    list = ["red", "orange", "green", "blue"]
if "red" in list:
    do_something()
  • Keyword "not" can be combined with "in".
  • Example:
    list = ["red", "orange", "green", "blue"]
if "purple" not in list:
    do_something()

• for and Lists
  • for loops can be used with lists just as they are with strings.
  • Example:
    email = ["you@email.com", "bob@email.com"]
for item in email:
    send_email()

• Other List Tricks
  • len(list_name)
    Gets the length of a list
  • list_name.sort()
    Built-in function to put lists in alphabetical order
  • random.choice(list_name)
    Picks a random item from a list.
  • string.split(list_name)
    Converts a string, like a sentence, into a list of words.
  • string.join(list_name)
    Converts a list of words it into a sentence in string form.
• Automatic Number list with range()
  • range():
  • Takes start number, end number, and step parameters
  • Returns a list of numbers
  • Examples:
    range(2,10) = [2,3,4,5,6,7,8,9]
range(0,11,2) = [0,2,4,6,8,10]
• Review
  • What is a list?
  • How does a list differ from a string?
  • What is a nested list?
  • What is mutability?
  • What special functions can be used with lists?