在 Python 中实例化多级 Inheritance 的问题

Question

In a particular sequence of a test case, there is a TypeError: __init__ error.

When I run this code with TestCode 3 before TestCode 2, there is a TypeError: __init__ .

If I run TestCode 3 after Test Code 2, there is no error and output is displayed. Why?

CODE:

import datetime

class Employee:

    def __init__(self, name="", salary=0, job_desc="", doj=None):
        self.name = name
        self.salary = salary
        self.description = job_desc
        self.dataOfJoing = doj
        self.no_of_years = ""

    def calRaise(self):
        today = datetime.date.today()
        self.no_of_years = today.year - self.dataOfJoing.year
        if int(self.no_of_years) > 5:
            percent = 0.20
        else:
            percent = 0
        self.salary = self.salary + (self.salary * percent)

    def display(self):
        return "Employee: name = %s, Job description= %s, No of years= %s, " \
               "Salary = %s" % (self.name, self.description, self.no_of_years, self.salary)



class Server(Employee):

    def __init__(self, name="", salary=0, job_desc="", doj=None):
        Employee.__init__(self, name, salary, job_desc, doj)


class chef(Employee):

    def __init__(self, name="", salary=0, job_desc="", doj=None):
        Employee.__init__(self, name, salary, job_desc, doj)


class PizzaRobot(chef):

    def __init__(self):
        chef.__init__(self, "Robot",0,"cooks",datetime.datetime(2012, 9, 10))

TestCode 1:

server = Server("John", 400, "customer interface", datetime.date(2015, 4, 3))

server.calRaise()

print(server.display())

TestCode 3:

chef = chef("Tom", 5000, "makes food", datetime.datetime(2000, 8, 13))

chef.calRaise()

print(chef.display())

TestCode 2:

robot = PizzaRobot()

robot.calRaise()

print(robot.display())

ERROR Message when TestCode 3 is run above TestCode 2:

Traceback (most recent call last): File "/Users/z10049/PycharmProjects/Q4Lab5/Q4.py", line 52, in robot = PizzaRobot() File "/Users/z10049/PycharmProjects/Q4Lab5/Q4.py", line 38, in init chef. init (self, "Robot",0,"cooks",datetime.datetime(2012, 9, 10)) TypeError: init () takes from 1 to 5 positional arguments but 6 were given

Answer 1

It's because you reuse the class name chef for the variable in this line:

chef = chef("Tom", 5000, "makes food", datetime.datetime(2000, 8, 13))

Then when you create the PizzaRobot object Python tries to call the __init__ method on the object created above on this line:

chef.__init__(self, "Robot",0,"cooks",datetime.datetime(2012, 9, 10))

When Python calls a method on an object it automatically passes the object itself as the first argument to the method. So it will essentially change the call above to:

chef.__init__(self, self, "Robot",0,"cooks",datetime.datetime(2012, 9, 10))

That's why you're getting the error about 6 arguments instead of 5.

If you rename the class chef to Chef and keep the variable as chef you'll see that everything will work as it should.