tals of Computer Science II home $>7\mathrm{.}9$: LAB: Grocery list editor with undo stack

$7\mathrm{.}9$ LAB: Grocery list editor with undo stack

In this lab a grocery list editor with undo functionality is implemented

Step $1$: Inspect the UndoCommand abstract base class

The read$-$only UndoCommand py file has a declaration for the UndoCommand abstract base class. Access UndoCommand py by clicking on the orange arrow next to

main.py at the top of the coding window. The UndoCommand class represents a command object$-$an object. that stores all needed information to execute an action at a later point in time. For this lab, a command object stores information to undo a grocery list change made by the user.

Step $2$: Inspect the incomplete GroceryList class

The GroceryList class is declared in

GroceryList.py$.$ Two attributes are declared

A list of strings for list items

A stack of UndoCommand references for undo commands

A simple list implementation of stack ADT is provided in Stack py

Note that the add with undo $0$ method is already implemented. The method adds a new item to the list and pushes a new

RemoveLastCommand object onto the undo stack

Step $3$: Implement RemoveLastCommand's execute$()$ method

The RemoveLastCommand class inherits from UndoCommand and is declared in RemoveLastCommand py$.$ When a RemoveLastCommand object is executed, the string list's last element is removed So when the user appends a new item to the grocery list, a RemoveLastCommand is pushed onto the stack of undo commands. Popping and executing the RemovelastCommand then removes the item most recently added by the user

RemoveLastCommand s source fist attribute and constructor are aiready declared

sotrce list is a reference to a Grocerylist objects list of strings

The constructor takes a reference to alist of strings as a parameter, and assigns source list with the reference

Implement RemoveLastCommand's execute$()$ method to remove source$\_$list's last element.

Step $4$: Implement GroceryList's execute$\_$undo$()$ method

of Computer Science II home $>7\mathrm{.}9$: LAB: Grocery list editor with undo stack

$0.$ bananas

The program's output does not affect grading, so additional test cases can be added, if desired.

Submitting code written so far to obtain partial credit is recommended before proceeding to the next step

Step $5$: Implement the SwapCommand class and GroceryList's swap$\_$with$\_$undo$()$ method

Implement the SwapCommand class in

SwapCommand.py$.$ The class itself is declared, but no attributes yet exist. Add necessary attribut and methods so that the command can undo swapping two items in the grocery list.

Implement GroceryList's swap$\_$with$\_$undo$()$ method. The method swaps list items at the specified indices, then pushes a SwapCommand, to undo that swap, onto the undo stack.

Step $6$: Implement the InsertAtCommand class and GroceryList's remove$\_$at$\_$with$\_$undo$()$ method

Implement the InsertAtCommand class in

InsertAtCommand.py$.$ Add necessary fields and methods so that the command can undo removing a grocery list item at an arbitrary index

Implement GroceryList's remove$\_$at$\_$with$\_$undo$()$ method. The method removes the list item at the specified index, then pushes an InsertAtCommand, to undo that removal, onto the undo stack.

$\left[\begin{array}{cc}\text{L}\text{A}\text{B}& 7\text{:}9\mathrm{.}1\text{:}\text{L}\text{A}\text{B}\text{:}\text{G}\text{r}\text{o}\text{c}\text{e}\text{r}\text{y}\text{l}\text{i}\text{s}\text{t}\text{e}\text{d}\text{i}\text{t}\text{o}\text{r}\text{w}\text{i}\text{t}\text{h}\text{u}\text{n}\text{d}\text{o}\text{s}\text{t}\text{a}\text{c}\text{k}\end{array}\right]$

$010$

Downioadable files

main.py$,$

Undocommand.py$,$

RemoveLastComand.py $,$

SwapCommand.py

InsertAtCommand,py $,$ Grocerylist,py and

Stack.py

Download

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$[1])$:$\}$

self. undo stack $=[$ Stack $(i)])$:$\}$

$[$ self Mist items append $(new$ item name$)$

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