def __init__(self, location):
        """Construct a new ContextFieldExistence object for a vertex field from the global context.

        Args:
            location: Location, specifying where the field was declared. Must point to a vertex.

        Returns:
            new ContextFieldExistence expression which evaluates to True iff the vertex exists
        """
        super(ContextFieldExistence, self).__init__(location)
        self.location = location
        self.validate()
def __init__ ( self , location ) : super ( ContextFieldExistence , self ) . __init__ ( location ) self . location = location self . validate ( )
Construct a new ContextFieldExistence object for a vertex field from the global context.

        Args:
            location: Location, specifying where the field was declared. Must point to a vertex.

        Returns:
            new ContextFieldExistence expression which evaluates to True iff the vertex exists