from abc import ABC, abstractmethod

class Shape(ABC):
    @abstractmethod
    def area(self):
        pass

class Circle(Shape):
    def __init__(self, r):
        self.r = r

c = Circle(5)
print(c.r)

class Manager:
    def __enter__(self):
        print("Begin", end=' ')
        return self

    def __exit__(self, exc_type, exc_val, exc_tb):
        print("End", end=' ')

    def work(self):
        print("Doing work", end=' ')

with Manager() as m:
    m.work()

class Catcher:
    def __enter__(self):
        print("Start", end=' ')
        return self

    def __exit__(self, exc_type, exc_val, exc_tb):
        print("Caught", end=' ')
        return True

with Catcher():
    print("Inside", end=' ')
    raise ValueError("Oops")
print("Done")

class Meta(type):
    def __new__(cls, name, bases, dct):
        print(f"Creating {name}", end=' ')
        return super().__new__(cls, name, bases, dct)

class A(metaclass=Meta):
    def __init__(self):
        print("Init A", end=' ')

print("Done")

class Meta(type):
    def __new__(cls, name, bases, dct):
        dct['greeting'] = 'Hello from metaclass'
        return super().__new__(cls, name, bases, dct)

class A(metaclass=Meta):
    pass

a = A()
print(a.greeting)

def join(*args, sep="-"):
    return sep.join(args)

print(join("a", "b", "c", sep="|"))

def make_funcs():
    return [lambda x: i * x for i in range(3)]

funcs = make_funcs()
print([f(2) for f in funcs])

def decorator(fn):
    def wrapper():
        return "Decorated " + fn()
    return wrapper

@decorator
def say():
    return "Hello"

print(say())

def apply(func, value):
    return func(value)

print(apply(abs, -5))

x = [(lambda y: y ** 2)(i) for i in range(3)]
print(x)

x = [(lambda y: y ** 2)(i) for i in range(3)]
print(x)