Here are descriptions of the three classes:

$**$LibraryItem:$**$

A LibraryItem object represents a library item that a patron can check out from a library. It has six data members:

$*$ library$\_$item$\_$id $-$ a unique identifier for a LibraryItem $-$ you can assume uniqueness, you don't have to enforce it

$*$ title $-$ cannot be assumed to be unique

$*$ location $-$ a LibraryItem can be $"$ON$\_$SHELF", $"$ON$\_$HOLD$\_$SHELF", or "CHECKED$\_$OUT"

$*$ checked$\_$out$\_$by $-$ refers to the Patron who has it checked out $($if any$)$

$*$ requested$\_$by $-$ refers to the Patron who has requested it $($if any$)$; a LibraryItem can only be requested by one Patron at a time

$*$ date$\_$checked$\_$out $-$ when a LibraryItem is checked out, this will be set to the current$\_$date of the Library

The LibraryItem methods are:

$*$ init method $-$ takes a library item ID and title as parameters; checked$\_$out$\_$by and requested$\_$by should be initialized to None; a new LibraryItem's location should be on the shelf

$*$ get$\_$location returns the Library Item's location

$*$ other get and set methods as needed

$**$Book$/$Album$/$Movie:$**$

$*$ These three classes all inherit from LibraryItem

$*$ All three will need an additional data member. For Book, it's a string called author. For Album, it's a string called artist. For Movie, it's a string called director

$*$ Each of the new data members will need a get method to return its value

$*$ All three will need a method called get$\_$check$\_$out$\_$length that returns the number of days that type of library item may be checked out for. For a Book it's $21$ days, for an Album it's $14$ days, and for a Movie it's $7$ days

$**$Patron:$**$

A Patron object represents a patron of a library. It has four data members:

$*$ patron$\_$id $-$ a unique identifier for a Patron $-$ you can assume uniqueness, you don't have to enforce it

$*$ name $-$ cannot be assumed to be unique

$*$ checked$\_$out$\_$items $-$ a collection of LibraryItems that a Patron currently has checked out

$*$ fine$\_$amount $-$ how much the Patron owes the Library in late fines $($measured in dollars$)$; this is allowed to go negative

The Patron methods are:

$*$ init method $-$ takes a patron ID and name as parameters

$*$ get$\_$fine$\_$amount $-$ returns the fine$\_$amount

$*$ other get and set methods as needed

$*$ add$\_$library$\_$item $-$ adds the specified LibraryItem to checked$\_$out$\_$items

$*$ remove$\_$library$\_$item $-$ removes the specified LibraryItem from checked$\_$out$\_$items

$*$ amend$\_$fine $-$ a positive argument increases the fine$\_$amount, a negative one decreases it; this is allowed to go negative

$**$Library:$**$

A Library object represents a library that contains variaous library items, and is used by various patrons. It has three data members:

$*$ holdings $-$ a collection of the LibraryItems that belong to the Library

$*$ members $-$ a collection of the Patrons who are members of the Library

$*$ current$\_$date $-$ stores the current date represented as an integer number of "days" since the Library object was created

The Library methods are:

$*$ an init method that initializes the holdings and members as empty collections and initializes the current$\_$date to zero

$*$ add$\_$library$\_$item $-$ takes a LibraryItem object as a parameter and adds it to the holdings

$*$ add$\_$patron $-$ takes a Patron object as a parameter and adds it to the members

$*$ lookup$\_$library$\_$item$\_$from$\_$id $-$ returns the LibraryItem object corresponding to the ID parameter, or None if no such LibraryItem is in the holdings

$*$ lookup$\_$patron$\_$from$\_$id $-$ returns the Patron object corresponding to the ID parameter, or None if no such Patron is a member

$*$ check$\_$out$\_$library$\_$item

$*$ takes as parameters a patron ID and a library item ID$,$ in that order

$*$ if the specified Patron is not in the Library's members, return "patron not found"

$*$ if the specified LibraryItem is not in the Library's holdings, return "item not found"

$*$ if the specified LibraryItem is already checked out, return "item already checked out"

$*$ if the specified LibraryItem is on hold by another Patron, return "item on hold by other patron"

$*$ otherwise update the LibraryItem's checked$\_$out$\_$by$,$ date$\_$checked$\_$out and location

$*$ if the LibraryItem was on hold for this Patron, update requested$\_$by

$*$ update the Patron's checked$\_$out$\_$items

$*$ return "check out successful"

$*$ return$\_$library$\_$item

$*$ takes as its parameter a library item ID

$*$ if the specified LibraryItem is not in the Library's holdings, return "item not found"

$*$ if the LibraryItem is not checked out, return "item already in library"

$*$ update the Patron's checked$\_$out$\_$items

$*$ update the LibraryItem's location depending on whether another Patron has requested it $($if so$,$ it should go on the hold shelf$)$

$*$ update the LibraryItem's checked$\_$out$\_$by

$*$ return "return successful"

$*$ request$\_$library$\_$item

$*$ takes as parameters a patron ID and a library item ID$,$ in that order

$*$ if the specified Patron is not in the Library's members, return "patron not found"

$*$ if the specified LibraryItem is not in the Library's holdings, return "item not found"

$*$ if the specified LibraryItem is already requested, return "item already on hol