import py

# ____________________________________________________________
# Example of building classes "manually", by calling type()

A = type("A", (object, ), {})     # 'object' is the base class

def f(a, z):
    return a.x + a.y + z

A.f = f      # 'f' is now a method in the class 'A'


B = type("B", (A, ), {})     # B inherits from A

def g(b):
    return b.x * 17

B.g = g

# ____________________________________________________________
# Example of building equivalent classes by using the
# normal syntax provided by Python

class A2(object):
    def __init__(self, x, y):     # constructor
        self.x = x
        self.y = y

    def f(self, z):
        return self.x + self.y + z

class B2(A2):
    def g(self):
        return self.x * 17

# ____________________________________________________________
# Test and implement an equivalent of the built-in
# issubclass() function:

def test_issubclass():
    assert my_issubclass(A, object)
    assert my_issubclass(B, object)
    assert my_issubclass(B, A)
    assert my_issubclass(A, A)
    assert my_issubclass(A, B) == False

def my_issubclass(subcls, cls):
    while subcls is not None:
        if subcls is cls:
            return True
        subcls = subcls.__base__       # note that object.__base__ is None
    return False

# ____________________________________________________________
# Test and implement an equivalent of the built-in
# isinstance() function:

def test_isinstance():
    a = A()
    b = B()
    assert my_isinstance(a, A)
    assert my_isinstance(a, object)
    assert my_isinstance(b, B)
    assert my_isinstance(b, A)
    assert my_isinstance(b, object)

    assert my_isinstance(a, B) == False
    assert my_isinstance(a, list) == False
    assert my_isinstance(1.1, list) == False

def my_isinstance(obj, cls):
    return my_issubclass(obj.__class__, cls)

# ____________________________________________________________
# Sending messages to objects

def test_send():
    a = A()
    a.x = 12
    a.y = 13
    assert a.f(1) == 26              # the normal Python syntax
    assert send(a, "f", 1) == 26     # the equivalent call to our send() below

    b = B()
    b.x = 14
    b.y = 15
    assert b.f(-1) == 28
    assert send(b, "f", -1) == 28
    assert b.g() == 14 * 17
    assert send(b, "g") == 14 * 17

def test_send2():
    # The same as test_send(), but using the classes A2, B2 instead of A, B
    a = A2(12, 13)
    assert a.f(1) == 26
    assert send(a, "f", 1) == 26

    b = B2(14, 15)
    assert b.f(-1) == 28
    assert send(b, "f", -1) == 28
    assert b.g() == 14 * 17
    assert send(b, "g") == 14 * 17

def test_send_message_not_found():
    # when a method is not found, we get an exception AttributeError
    a = A()
    a.x = 12
    a.y = 13
    py.test.raises(AttributeError, "a.notthere(1)")
    py.test.raises(AttributeError, "send(a, 'notthere', 1)")
    # Remark: py.test.raises() tries to execute the piece of code given
    # as a string, and checks that it raises the specified exception

def send(obj, message, *args):
    # 'message' is a string, looked up in the class of 'obj'
    cls = obj.__class__
    while cls is not None:
        if message in cls.__dict__:     # does the class have this method?
            method = cls.__dict__[message]
            # 'method' is really a function object: insert 'obj' as 1st arg
            return method(obj, *args)
        cls = cls.__base__
    raise AttributeError(obj.__class__.__name__ + " object does not have attribute " + message)