इंस्टेंस विधियाँ और self

class Circle:
    def __init__(self, r): self.r = r
    def area(self):
        import math
        return math.pi * self.r**2
print(Circle(5).area())

class Dog:
    def __init__(self, name): self.name = name
    def bark(self): print(f'{self.name} says Woof!')
Dog('Rex').bark()

class Builder:
    def __init__(self): self.data = {}
    def set(self, k, v):
        self.data[k] = v
        return self
    def build(self): return self.data
result = Builder().set('x',1).set('y',2).build()
print(result)

class Account:
    def __init__(self, bal): self._bal = bal
    def _validate(self, amount): return amount > 0
    def deposit(self, amount):
        if self._validate(amount):
            self._bal += amount
a = Account(100)
a.deposit(50)
print(a._bal)

class Circle:
    def __init__(self, r): self.r = r
    @property
    def diameter(self): return self.r * 2
c = Circle(5)
print(c.diameter)  # no ()

class Stack:
    def __init__(self): self.items = []
    def push(self, x): self.items.append(x)
    def pop(self): return self.items.pop()
    def peek(self): return self.items[-1]
s = Stack()
s.push(1); s.push(2)
print(s.pop(), s.peek())

class Point:
    def __init__(self, x, y): self.x,self.y=x,y
    def __eq__(self, other): return self.x==other.x and self.y==other.y
print(Point(1,2)==Point(1,2))

class Countdown:
    def __init__(self, n): self.n = n
    def __iter__(self): return self
    def __next__(self):
        if self.n <= 0: raise StopIteration
        self.n -= 1; return self.n + 1
print(list(Countdown(3)))

class Timer:
    def __enter__(self):
        import time
        self.start = time.time()
        return self
    def __exit__(self, *args):
        import time
        print(f'elapsed: {time.time()-self.start:.3f}s')
with Timer(): pass

class Dog:
    def bark(self): print('woof')
print(type(Dog.bark))
print(type(Dog().bark))