def grad_not_implemented(op, x_pos, x, comment=''):
 return NullType(('This variable is Null because the grad method for input %s (%s) of the %s op is not implemented. %s' % (x_pos, x, op, comment)))()

def grad_not_implemented ( op , x_pos , x , comment = '' ) : return NullType ( ( 'This variable is Null because the grad method for input %s (%s) of the %s op is not implemented. %s' % ( x_pos , x , op , comment ) ) ) ( )
return an un-computable symbolic variable of type x .