#PYTHON(DAY21)instance,static attributes and methods

 

#PYTHON(DAY21)

instance attributes

• object level attribute
• these may or may not have the same values across all objects
• in above example, the crust,oil etc can have different values for different objects, these can be considered as instance attributes

class Foo:
    def __init__(self, a, b):
        self.a = a
        self.b = b
x1,x2 = Foo(10,20), Foo(11,22)
print((x1.a,x1.b), (x2.a,x2.b), sep = '\n')

And the output is:

(10, 20)
(11, 22)

static attributes

• static variable remains common for the entire class
• the user can change according to his requirement

class Rest:
    disc = 0
    def __init__(self,bill):
        self.bill = bill
        
   
    def totalBill(self):
        return self.bill-(self.bill*self.disc)

a1 = Rest(50)
print(a1.totalBill())

a2 = Rest(50)
a2.disc = 0.10
a2.totalBill()

And the output is:

50
45.0

methods

instance methods

• these methods take self as first parameter, we use these methods to modify or alter the instance’s attributes or state
• in dictionary from keys is a class method and all are instance methods.
• instance method acts on object, attributes changes on object level

class methods

• these methods accepts ‘cls’ as their first attribute, we define a class method by using a decorator @classmethod
• class method acts on class level
• using class method we can alter class attributes

static methods

• we define static methods using @staticmethod decorator, these methods accept no cls or self as first parameter
• it does not work on class or object

class Rest:
    disc = 0
    def __init__(self,bill):
        self.bill = bill
        
    def printBill(self):
        print(f'bill before discount is {self.bill}')
        
    @classmethod
    def discount(cls):
        print(f'the discount you availed is{cls.disc} %')
        #print(f'total bill to paidmpost discount is {self.})
    @staticmethod
    def greet():
        print('welcome')

Rest.discount()

# using the object
a1 = Rest(50)
a1.printBill()
a1.discount() # we can also access class attribute by using object without self

And the output is:

the discount you availed is0 %
bill before discount is 50
the discount you availed is0 %

a1.greet()
Rest.greet()

And the output is:

welcome
welcome

class student1():
    y = 60
    def details(self,name,rollno,study,sec,totalmarks):
        self.n = name
        self.r = rollno
        self.a = study
        self.sec = sec
        self.m = totalmarks
        
    def cutoff(self):
        if self.m>=self.y:
            print('pass')
        else:
            print('fail')
    def over(self):
        print((f'''student name is {self.n} rollno:{self.r} belongs to {self.a}class section {self.sec} total marks are {self.m}'''))

ab = student1()
ab.details('xyz',456,7,'a',50)
ab.cutoff()
ab.over()

fail
student name is xyz rollno:456 belongs to 7class section a total marks are 50