old_contents: """Mutual exclusion -- for use with module sched
  
  A mutex has two pieces of state -- a 'locked' bit and a queue.
  When the mutex is not locked, the queue is empty.
  Otherwise, the queue contains 0 or more (function, argument) pairs
  representing functions (or methods) waiting to acquire the lock.
  When the mutex is unlocked while the queue is not empty,
  the first queue entry is removed and its function(argument) pair called,
  implying it now has the lock.
  
  Of course, no multi-threading is implied -- hence the funny interface
  for lock, where a function is called once the lock is aquired.
  """
  from warnings import warnpy3k
  warnpy3k("the mutex module has been removed in Python 3.0", stacklevel=2)
  del warnpy3k
  
  from collections import deque
  
  class mutex:
      def __init__(self):
          """Create a new mutex -- initially unlocked."""
          self.locked = 0
          self.queue = deque()
  
      def test(self):
          """Test the locked bit of the mutex."""
          return self.locked
  
      def testandset(self):
          """Atomic test-and-set -- grab the lock if it is not set,
          return True if it succeeded."""
          if not self.locked:
              self.locked = 1
              return True
          else:
              return False
  
      def lock(self, function, argument):
          """Lock a mutex, call the function with supplied argument
          when it is acquired.  If the mutex is already locked, place
          function and argument in the queue."""
          if self.testandset():
              function(argument)
          else:
              self.queue.append((function, argument))
  
      def unlock(self):
          """Unlock a mutex.  If the queue is not empty, call the next
          function with its argument."""
          if self.queue:
              function, argument = self.queue.popleft()
              function(argument)
          else:
              self.locked = 0
  
new_contents: """Mutual exclusion -- for use with module sched
  
  A mutex has two pieces of state -- a 'locked' bit and a queue.
  When the mutex is not locked, the queue is empty.
  Otherwise, the queue contains 0 or more (function, argument) pairs
  representing functions (or methods) waiting to acquire the lock.
  When the mutex is unlocked while the queue is not empty,
  the first queue entry is removed and its function(argument) pair called,
  implying it now has the lock.
  
  Of course, no multi-threading is implied -- hence the funny interface
  for lock, where a function is called once the lock is aquired.
  """
  from warnings import warnpy3k
  warnpy3k("the mutex module has been removed in Python 3.0", stacklevel=2)
  del warnpy3k
  
  from collections import deque
  
  class mutex:
      def __init__(self):
          """Create a new mutex -- initially unlocked."""
          self.locked = False
          self.queue = deque()
  
      def test(self):
          """Test the locked bit of the mutex."""
          return self.locked
  
      def testandset(self):
          """Atomic test-and-set -- grab the lock if it is not set,
          return True if it succeeded."""
          if not self.locked:
              self.locked = True
              return True
          else:
              return False
  
      def lock(self, function, argument):
          """Lock a mutex, call the function with supplied argument
          when it is acquired.  If the mutex is already locked, place
          function and argument in the queue."""
          if self.testandset():
              function(argument)
          else:
              self.queue.append((function, argument))
  
      def unlock(self):
          """Unlock a mutex.  If the queue is not empty, call the next
          function with its argument."""
          if self.queue:
              function, argument = self.queue.popleft()
              function(argument)
          else:
              self.locked = False
  
subject: use True and False