program is:

class Stud:
    def __init__(self):
        self.displval()
        print("I am Constructor")    
        self.sno = int(input("Enter the roll number"))
        self.sname = (input("Enter the Name"))
    def displval(self):
        print("="*50)
        print(self.sno)
        print(self.sname)

so = Stud() 

CodePudding user response：

Your main problem is that you are calling self.displval before you set the attributes it tries to display.

class Stud:
    def __init__(self):
        print("I am Constructor")    
        self.sno = int(input("Enter the roll number"))
        self.sname = (input("Enter the Name"))
        self.displval()

    def displval(self):
        print("="*50)
        print(self.sno)
        print(self.sname)

However, __init__ is doing too much work. It should receive values as arguments and simply set the attributes. If you want Stud to provide a way to collect those arguments from the user, define an additional class method. (It's also debatable whether __init__ should be printing anything to standard output, but I'll leave that for now.)

class Stud:
    def __init__(self, sno, sname):
        self.sno = sno
        self.sname = sname
        self.displval()

    @classmethod
    def create_with_user_input(cls):
        sno = int(input("Enter the roll number"))
        sname = (input("Enter the Name"))
        return cls(sno, sname)

    def displval(self):
        print("="*50)
        print(self.sno)
        print(self.sname)

so = Stud.create_from_user_input()

CodePudding user response：

class Stud:
    def __init__(self):

        print("I am Constructor")
        self.sno = int(input("Enter the roll number"))
        self.sname = (input("Enter the Name"))
        self.displval()

    def displval(self):
        print("="*50)
        print(self.sno)
        print(self.sname)

so = Stud()

Put the self.displval() at the end. You're calling it before it has any self.[value] to pass into the method.