about the implementations of these classes, public methods defined in by the Stack or queve ADTs.

$(9)316x^3{?}^{{?}^{?}}$

$($Refer to the readings if you aren't sure what these are.$)$

In particular, this means that you shouldn't try to access any attributes of either class, since the ADT descriptions only define what $($methods$)$ can be used for the ADTs.

GENERAL HINT: save values in local variables! Even if you pop an item off of a stack, it's not "gone forever" if you assign it to a variable. $"""$

import

$1$ usage

def peek$($stack: Stack$)$ Optional$[$Any$]$:

$""$ "Return the top item on the given stack.

If the stack is empty, return None.

Unlike Stack.pop, this function should leave the stack unchanged when the function ends. You can $($and should$)$ still call pop and push, just make sure that if you take any items off the stack, you put them back on$!$

$$ stack $=$ stack$()$