Announcements

• GL with the midterm
• Y'all will do great!
• Cats checkpoint due today
• Cats due on next Tuesday

Comments from last section

• Cover more stuff on discussion worksheets
• How do you reverse a tree
  • 
  • depends on what implementation of trees you're using (the 61a version is a bit harder, but still possible with the reverse function)
    • ask me over email, i'll send over something
  • Do you have a favorite cat breed?
    • I like all cat breeds (even the hairless ones are cute )
  • how tall are you？recursion and leap of faith and tuples!!!
    • im 180cm (i think that's 5'11")
    • we can get to the other stuff once we hit midterm review

Comments from last section

• how many pushups can u do
  • 
• Definitely some extra review on trees
  • got some during lab, might get some more today!
• Dr Pepper >> Coca cola
  • still haven't tried dr pepper (maybe)
• In the game Enter the Gungeon, there is one NPC you can only understand if you have a specific item. He is very eleoquent
  • bullet hell games!! hard

Temperature Check

• Iterators
• Generators

Iterators

• Iterable
  • Old View: Something we can go through one at a time
  • New View: Something we can call iter on - this will return an iterator.
• Iterator
  • A type of object that lets us keep track of which element is next in the sequence

Functions to Interact with Iterators

• iter(iterable)
  • Takes in an iterable and returns an iterator.
    • Calling iter on an iterable makes a brand new iterator
    • Calling iter on an iterator returns that same iterator (not a copy!) and does not change the state of that iterator
• next(iterator)
  • Takes in an iterator and outputs the next element
    • Raises StopIteration when it has no more elements to go through
    • Cannot call next on an iterable

Analogy

• Iterable = Book
• Iterator = Bookmark
• Calling iter on an iterable (book) will create a new bookmark
• Calling iter on an iterator (bookmark) will just give you the same bookmark (no reason to mark where a bookmark is)
• Calling next on an iterator moves the bookmark to the next chapter

do some terminal example pls thx

Generators

• Generators are more specific versions of iterators that you can create yourself!
• When a generator function is called, it returns a generator object!
• The body of a generator function is not evaluated until next is called on the returned generator object.
• Generator functions look like normal functions, but use yield instead of return. Python will automatically see yield and determine a function a generator function if necessary.

Generators (continued)

• When next is called on a generator object, the body of a function is executed until yield is reached.
• From there, the yield statement will return a value, and then pauses that specific function at that moment (by saving the frame, and the line that it's on)
• When next is called again, we continue where we left off, until yield is reached again.
• StopIteration will be raised at the end of a generator function

Example

yield from

• You can use yield from <iterable> if you want to yield every value from an iterable. These are equivalent:

Midterm tips

• Studying
• Question annotation
• Example Question (Fall 2021 MT2 amounts)

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