class AbstractCollection:

def init$($self$,$ source$\_$collection$=$None$)$:

$"""$ Sets the initial state of self, which includes the contents of source$\_$collection $"""$

self.$\_$size $=0$

if source$\_$collection:

for item in source$\_$collection:

self.add$($item$)$

def len$($self$)$:

$"""$ Return the number of items in this collection $"""$

return self.$\_$size

def is$\_$empty$($self$)$:

$"""$ Returns True if the collection is empty and False otherwise $"""$

return len$($self$)==0$

def add$($self$,$ other$)$:

$"""$ Overloads the $+$ operator. A new collection is created with everything from self and other. $"""$

result $=$ type$($self$)($self$)$

for item in other:

result.add$($item$)$

return result

class Node:

$"""$ Represents a Node in a singly$-$linked list $"."$

def init$($self$,$ data, next$=$None$)$:

$"""$ By default, this Node will not link to another Node $"""$

self.data $=$ data

self.next $=$ next

class BinaryNode:

$"""$ Represents a Node in a binary tree $"""$

def init$($self$,$ data, left$=$None, right$=$None$)$:

$"""$ By default, this Node will not have any children $"""$

self.data $=$ data

self.left $=$ left

self.right $=$ right