Inheritance and Decorators in Python
Source Code
Classes
Admin is a child of User: it inherits the instance properties name and is_logged_in.
class User:
def __init__(self, name):
self.name = name
self.is_logged_in = False
class Admin(User):
def __init__(self, name):
super().__init__(name)
Post in reality would never have a randomnly generated id, but would receive its ID from a posts table in the database.
I have yet to learn the Django equivalent of a Model in Ruby on Rails.
class Post:
def __init__(self, id=None):
self.id = id or random.randint(0, 1000)
Decorator Functions
is_authenticated checks the is_logged_in instance attribute of the object.
def is_authenticated(function):
def wrapper(*args):
if args[0].is_logged_in is True:
return function(*args)
else:
raise Exception("401")
return wrapper
is_admin checks whether the object itself isinstance of Admin.
def is_admin(function):
def wrapper(*args, **kwargs):
if isinstance(args[0], Admin):
return function(*args, **kwargs)
else:
raise Exception("401")
return wrapper
Functions with Class Instance Objects
create_blog_post can be performed by either User or Admin providing he is_authenticated, i.e. is_logged_in:
@is_authenticated
def create_blog_post(user):
print(f"This is {user.name}'s new blog post.")
return {"status": "ok"}
delete_blog_post can be performed only by an Admin`` who is_logged_in.
@is_admin
@is_authenticated
def delete_blog_post(user, post):
print(f"{user.name} deleted post {post.id}")
return {"status": "ok"}
Testing
Fixtures
Testing requires setup of Class Instance objects in a certain state – logged in or not, admin or not.
This is trickier than using primitives are objects with a fixed state, both in setup and execution of the tests.
Test scenarios require user_with_login, user_sans_login, admin_with_login. Admin not logged in is identical to a User not logged in, so both cases are covered by user_sans_login. An instance of Post is also required to test a successful execution of delete_blog_post(user, post).
@pytest.fixture
def user_with_login():
u = d.User("Foo")
u.is_logged_in = True
yield u
@pytest.fixture
def user_sans_login():
u = d.User("Bar")
print(u.name)
print(u.is_logged_in)
yield u
@pytest.fixture
def admin_with_login():
u = d.Admin("MyAdmin")
u.is_logged_in = True
yield u
@pytest.fixture
def my_post():
post = d.Post(42)
yield post
Tests
Tests are filtered by a custom tag filter and the command pytest -k filter or ptw -- -k filter.
@pytest.mark.filter
def test_authenticated(user_with_login):
assert user_with_login.is_logged_in is True
assert d.create_blog_post(user_with_login) == {"status": "ok"}
@pytest.mark.filter
def test_unauthenticated(user_sans_login):
assert user_sans_login.is_logged_in is False
with pytest.raises(Exception) as e:
d.create_blog_post(user_sans_login)
assert e.value == "401"
@pytest.mark.filter
def test_authenticated_admin(admin_with_login, my_post):
assert admin_with_login.is_logged_in is True
assert isinstance(admin_with_login, d.Admin) is True
assert my_post.id == 42
assert d.delete_blog_post(admin_with_login, my_post) == {"status": "ok"}
@pytest.mark.filter
def test_authenticated_not_admin(user_with_login, my_post):
assert user_with_login.is_logged_in is True
assert isinstance(user_with_login, d.User) is True
assert my_post.id == 42
with pytest.raises(Exception) as e:
d.delete_blog_post(user_with_login, my_post)
assert e.value == "401"