old_contents: class CameraError(Exception):
  	def __init__(self, msg, cam):
  		self.msg = msg
  		self.camera_number = cam
  	
  	def __str__(self):
  		return '{0} on camera {1}'.format(self.msg, self.camera_number)
  
  class Camera(object):
      def __init__(self, cam=-1):
          self.camera_number = cam
          self.frame = None
  
  	def __enter__(self):
  		self.open()
  		return self
  
      def __exit__(self, type, value, traceback):
          self.close()
          return False # don't suppress exceptions
  
      def open(self):
          raise NotImplementedError()
      
      def close(self):
          raise NotImplementedError()
      
      def query_frame(self):
          raise NotImplementedError()
          
      @property
      def resolution(self):
          raise NotImplementedError()
      
new_contents: class CameraError(Exception):
      def __init__(self, msg, cam):
          self.msg = msg
          self.camera_number = cam
  
      def __str__(self):
          return '{0} on camera {1}'.format(self.msg, self.camera_number)
  
  class Camera(object):
      def __init__(self, cam=-1):
          self.camera_number = cam
          self.frame = None
  
      def __enter__(self):
          self.open()
          return self
  
      def __exit__(self, type, value, traceback):
          self.close()
          return False # don't suppress exceptions
  
      def open(self):
          raise NotImplementedError()
  
      def close(self):
          raise NotImplementedError()
  
      def query_frame(self):
          raise NotImplementedError()
  
      @property
      def resolution(self):
          raise NotImplementedError()
  
subject: Fix indentation