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cs_disc_1017

#r/discussion

  • Discussion notes: link

Discussion 10 /17

print("Hello world i am cool")

We see that 

class Rational:
    def __init__(self,numerator,denominator):
        self.numerator = numerator
        self.denominator = denominator
    def __str__(self):
        return f'{self.numerator}/{self.denominator}'
    def __repr__(self):
        return

review from last class

Linked List Is either empty or a first value and the rest of the linked list link = Link(1,Link(2)) link -> (first) (rest)->[ first rest]

What is Link.empty? It's a class attribute equal to an empty tuple

What are the instance attributes? .first- a value like the label of a tree .rest - a linked list or Link.empty. Link.rest.first for example will refer to the instance attribute.

Traversing Linked Lists (iteratively(use pointers))

pointer = lnk
while lnk!=Link.empty
    pointer = pointer.rest

Note: always pay attention to mutation vs creation Mutation: Changing the attrubtes of Link, such as changing what Link.first is Creation: Creating a new Linked List using the Link() constructor

![[Code_L9BdmkmSYS.png]]

Linked list property

  • Link.first is a value
  • Link.rest is pointed to another Linked List. This can be itself(in which case the Linked List is effectively an infinite loop of values) or it can be another linked list.

Infinite Loop of Linked List: ![[chrome_VryKFI14GY.png]]

Essentially, every Linked List is just a pointer

There is a big difference between mutating an object and creating a new, mutated object: Assuming a function has parameter t, which is a tree: t = Tree(prod,t.branches) Creating a new (local) instance t, nothing to do with the passed in parameter t t.label = prod Manipulating the parameter t instance itself. In this case, to manipulate (mutate) the object, we must do the second option.