Valid Locking Schedule

Write a function, named $$validate$\_$locking$\_$schedule$$ that takes a list of Actions $($see below$)$ as its only parameter. This function doesn$$t return anything, but instead raises exceptions if the schedule is invalid $($according to legality of schedules, two$-$phased locking, and consistency of transactions$).$ Be sure to validate the actions in that order. The exception classes are already defined for you in your starter solution.

The Action class is a simple class with attributes denoting the id of the database object $($region$),$ the id of the transaction the action takes place in$,$ and the type of action $($if the action was a read, write, lock, or unlock$).$

You can assume the action class$$s object$\_$ and transaction attributes are strings or integers $($types which support equality$)$ and the type is an UPPERCASE string.

class Action:

$"""$

This is the Action class. It is already in the test cases, so please don't

put it in your solution.

$"""$

def $\_\_$init$\_\_($self$,$ object$\_,$ transaction, type$\_)$:

self.object$\_=$ object$\_$

self.transaction $=$ transaction

assert type$\_$ in $("$READ$",$ "WRITE", "LOCK", "UNLOCK"$)$

self.type$\_=$ type$\_$

def $\_\_$str$\_\_($self$)$:

return f$"$Action$(\{$self$.$object$\_\},\{$self$.$transaction$\},\{$self$.$type$\_\})"$

class LegalityOfScheduleViolation$($Exception$)$: pass

class TwoPhasedLockingViolation$($Exception$)$: pass

class ConsistencyOfTransactionViolation$($Exception$)$: pass

# Do not modify code above this line

def validate$\_$locking$\_$schedule$($actions$)$:

locks $=$ set$()$

transactions $=\{\}$

for action in actions:

if action.type$\_==$ "LOCK":

if action.object$\_$ in locks:

raise LegalityOfScheduleViolation$($f$"$Locking violation: Object $\{$action$.$object$\_\}$ is already locked."$)$

locks.add$($action$.$object$\_)$

elif action.type$\_==$ "UNLOCK":

if action.object$\_$ not in locks:

raise LegalityOfScheduleViolation$($f$"$Unlocking violation: Object $\{$action$.$object$\_\}$ is not locked."$)$

locks.remove$($action$.$object$\_)$

elif action.type$\_==$ "READ" or action.type$\_==$ "WRITE":

if action.transaction in transactions:

if action.object$\_$ in transactions$[$action$.$transaction$]$:

raise ConsistencyOfTransactionViolation$($f$"$Consistency violation: Transaction $\{$action$.$transaction$\}$ performs multiple operations on object $\{$action$.$object$\_\}.")$

else:

transactions$[$action$.$transaction$].$add$($action$.$object$\_)$

else:

transactions$[$action$.$transaction$]=$ set$([$action$.$object$\_])$

if locks:

raise TwoPhasedLockingViolation$("$Two$-$phased locking violation: Some objects are still locked at the end of the schedule."$)$

fail:

def test$\_$visible$\_3($self$)$:

# $($Two$-$Phased Locking$)$

actions $=[$

Action$($object$\_="$A$",$ transaction$="$T$2",$ type$\_=$"LOCK"$),$

Action$($object$\_="$B$",$ transaction$="$T$2",$ type$\_=$"LOCK"$),$

Action$($object$\_="$C$",$ transaction$="$T$2",$ type$\_=$"LOCK"$),$

Action$($object$\_="$D$",$ transaction$="$T$2",$ type$\_=$"LOCK"$),$

Action$($object$\_="$D$",$ transaction$="$T$2",$ type$\_=$"UNLOCK"$),$

Action$($object$\_="$E$",$ transaction$="$T$2",$ type$\_=$"LOCK"$),$

Action$($object$\_="$E$",$ transaction$="$T$2",$ type$\_=$"UNLOCK"$),$

Action$($object$\_="$A$",$ transaction$="$T$2",$ type$\_=$"UNLOCK"$),$

Action$($object$\_="$C$",$ transaction$="$T$2",$ type$\_=$"UNLOCK"$),$

Action$($object$\_="$B$",$ transaction$="$T$2",$ type$\_=$"UNLOCK"$),$

$]$

print$("$

Actions:"$)$

pprint$($actions$)$

with self.assertRaises$($TwoPhasedLockingViolation$)$:

validate$\_$locking$\_$schedule$($actions$)$

print$("$Correctly raised TwoPhasedLockingViolation"$)$

actions $=[$

Action$($object$\_="$A$",$ transaction$="$T$2",$ type$\_=$"LOCK"$),$

Action$($object$\_="$B$",$ transaction$="$T$2",$ type$\_=$"LOCK"$),$

Action$($object$\_="$A$",$ transaction$="$T$2",$ type$\_=$"UNLOCK"$),$

Action$($object$\_="$A$",$ transaction$="$T$1",$ type$\_=$"LOCK"$),$

Action$($object$\_="$B$",$ transaction$="$T$2",$ type$\_=$"UNLOCK"$),$

Action$($object$\_="$A$",$ transaction$="$T$1",$ type$\_=$"UNLOCK"$),$

$]$

print$("$

Actions:"$)$

pprint$($actions$)$

validate$\_$locking$\_$schedule$($actions$)$

print$("$Correctly didn't raise exception"$)$

error:

def test$\_$visible$\_2($self$)$:

# Legality of Schedules: locks block other locks$)$

actions $=[$

Action$($object$\_="$A$",$ transaction$="$T$2",$ type$\_=$"LOCK"$),$

Action$($object$\_="$A$",$ transaction$="$T$2",$ type$\_=$"READ"$),$

Action$($object$\_="$A$",$ transaction$="$T$2",$ type$\_=$"UNLOCK"$),$

Action$($object$\_="$A$",$ transaction$="$T$1",$ type$\_=$"LOCK"$),$

Action$($object$\_="$A$",$ transaction$="$T$1",$ type$\_=$"UNLOCK"$),$

$]$

print$("$

Actions:"$)$

pprint$($actions$)$

validate$\_$locking$\_$schedule$($actions$)$

print$("$Correctly didn't raise exception"$)$

actions $=[$

Action$($object$\_="$A$",$ transaction$="$T$2",$ type$\_=$"LOCK"$),$

Action$($object$\_="$B$",$ transaction$="$T$1",$ type$\_=$"LOCK"$),$

Action$($object$\_="$A$",$ transaction$="$T$2",$ type$\_=$"READ"$),$

Action$($object$\_="$A$",$ transaction$="$T$2",$ type$\_=$"UNLOCK"$),$

Action$($object$\_="$B$",$ transaction$="$T$1",$ type$\_=$"UNLOCK"$),$

$]$

print$("$Actions:$")$

pprint$($actions$)$

validate$\_$locking$\_$schedule$($actions$)$

print$("$Okay to repeatedly request to lock and unlock"$)$

give code