Missing 1 required positional argument in python Constructor

Question

I'm trying to learn inheritance concept in python. I have an Employee class and derivative class Executive.

class Employee:
    'Class defined for employee'

    def __init__(self, name, dept, salary):
        self.name = name
        self.dept = dept
        self.salary = salary

Subclass

class Executive(Employee):

    def __init__(self, name, dept, salary, hascar):
        Employee.__init__(name, dept, salary)
        self.hascar = hascar

has car is a Boolean passed into the constructor, However this will give me an error:

File "I:\Python_practicals\com\python\oop\Executive.py", line 7, in init Employee.init(name, dept, salary) TypeError: init() missing 1 required positional argument: 'salary'

When I try to Instantiate an object of Executive.
emp4 = Executive("Nirmal", "Accounting", 150000, True)

Jonathon Reinhart · Accepted Answer · 2018-09-18 14:39:54Z

7

While __init__ is an instance method, you're calling it on the class rather than on an instance. This invocation is called unbound, because it is not bound to an instance. Because of this, you need to explicitly pass self:

class Executive(Employee):
    def __init__(self, name, dept, salary, hascar):
        Employee.__init__(self, name, dept, salary)
#                         ^^^^
        self.hascar = hascar

The recommended way, however, is to use super:

Return a proxy object that delegates method calls to a parent or sibling class of type. This is useful for accessing inherited methods that have been overridden in a class.

With super your code would look like this:

class Executive(Employee):

    def __init__(self, name, dept, salary, hascar):
        super(Executive, self).__init__(name, dept, salary)
#       ^^^^^^^^^^^^^^^^^^^^^^
        self.hascar = hascar

Python 3 adds some syntactic sugar to make this common parent class invocation simpler:

class Executive(Employee):

    def __init__(self, name, dept, salary, hascar):
        super().__init__(name, dept, salary)  # Py 3
#       ^^^^^^^
        self.hascar = hascar

edited Sep 18, 2018 at 14:39

answered Sep 18, 2018 at 11:49

Jonathon Reinhart

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3 Comments

Vineeth Sai Over a year ago

In case python3 super() has much simpler syntax. super().__init__(name, dept, salary)

Jonathon Reinhart Over a year ago

I'm aware, but the OP tagged the question Python 2.7 so I have started with the compatible syntax.

Vineeth Sai Over a year ago

Oh haven't seen that. Sorry !. he also tagged python 3.x for some reason

Vineeth Sai · Accepted Answer · 2018-09-18 12:18:53Z

1

In Python 3.x
Use super() keyword. This will let you avoid typing the Base class explicitly. makes the code more maintainable.

class Executive(Employee):

    def __init__(self, name, dept, salary, hascar):
        super().__init__(name, dept, salary)
        self.hascar = hascar

edited Sep 18, 2018 at 12:18

answered Sep 18, 2018 at 11:52

Vineeth Sai

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