@observe('dob')
    def update_age(self, change):
        """ Update the person's age whenever their date of birth changes

        """
        # grab the current date time
        now = datetime.datetime.utcnow()
        # estimate the person's age within one year accuracy
        age = self.dob.year - now.year
        # check to see if the current date is before their birthday and
        # subtract a year from their age if it is
        if now.month >= self.dob.month and now.day > self.dob.day:
            age -= 1
        # set the persons age
        self.age = age
dataset/ETHPy150Open nucleic/enaml/examples/tutorial/employee/employee.py/Person.update_age/swapped operands of `-`