Announcements

• Cats got released
  • Be on the lookout for question 7 - start early, and start often
  • Getting started videos
• No HW released this week!

Comments from last section

• Do you like Cheese?
  • big yes
• How to get better at reading python output
  • good question tbh
  • error messages
  • debugging page
• Address more environment diagrams
  • for this point in the course (recursion), environment diagrams start being a bit worse
  • they'll come back eventually

Comments from last section

• Do you watch anime? If so, what's your favorite (or the one you like the most right now)?
  • i only watch the pokemon anime, and only do this occasionally (however it do be kinda hype)
• How many hours of sleep do you get per night? Are you a night owl or morning lark? Hope your classes are going well!
  • 7-8; prefer night, but i shift between both depending on what i have to do that day; classes are not going well
• If you could upload lab notes on to your website that would be great!
  • they're on the website!

Temperature Check

• Recursion
• Tree Recursion
• for loops
• Lists
  • List Comprehensions
• Dictionaries

Tree Recursion

• Tree recursion is recursion but with two (or more!) recursive calls
• Useful when you need to break down a problem in more than 1 way
• Useful when there are multiple choices to deal with at one function call
• The recursive call diagram will expand similar to the roots of a tree

Example 1: Recursive Fibonacci

• Notice how this still follows the rules of recursion
  • We have base case(s)
  • We reduce our problem (fib(n - 1) and fib(n - 2))
  • We connect it together (with +)
• Often you combine things with +, -, *, / or some other function (max, min, etc).

Example 1: Recursive Fibonacci

You can also write down

Lists

• So far, we've only really been able to store one piece of data at a time
• A list allows you to store multiple pieces of data in 1 variable
• Lists can store any data type, and can be a mix of different data types
  • For example: [1, "hello", [2, "hi"]]
• Very useful for storing data/information

Creating Lists

In general, to create a list, you wrap something in square brackets

• For example: [1, 2, 3] creates a list.

(List) Slicing

Syntax is lst[<start index>:<end index>:<step>]; this creates a copy of all or part of your list (will be important later)

• start index is inclusive (if not included, it defaults to the first value)
• end index is exclusive (if not included, it defaults to the end of the list)
• step can be negative!

For loops

Example:

List Comprehensions

Very similar to for loops, but can be done in 1 line!

Dictionaries

• Maps keys to values
  • keys must be 'hashable'
    • you can just think of keys needing to be immutable, but this is not too important
• values can be anything (including other dictionaries)
• Doesn't really have an order
• Access elements using keys rather than indices

Dictionaries

• Maps keys to values
• Doesn't really have an order
• Access elements using keys rather than indices
• Defined with curly braces ({})
  • {key: value}

Demo:

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