Python中的BaseBean反模式

Question

Background: Coming from Perl world, I'm currently learning Python in my new job. Apart from doing the work, I'm also trying to get more of "real OOP" and "pythonic" thinking into my brain cell flow, mostly by reading SO, Python docs and various articles.

Now in OO design section of Anti-pattern page, Wikipedia lists this BaseBean , which on its own page is described as:

In object-oriented programming, a BaseBean is a utility object from which concrete entities are derived (via subclassing). Proper design suggests that the inherited functionality should be provided via delegation instead. The BaseBean is an example of an anti-pattern (where the "Bean" part of the name comes from the standard Java naming convention for a generic entity object, or JavaBean).

Maybe it's because I have no experience with Java, maybe it's for other reason, but I'm having trouble wrapping my head around this explanation. However, I'm feeling that few lines of code would be worth thousand words here.

Could anyone help clarify this for me? Preferably using a simple example in Python?

Answer 1

Based on this quote in the Wikipedia article:

Using inheritance causes the derived class to rely on the internals of a base class which may be out of the control of the developer. While the utility classes are typically stable and fairly similar across implementations, some innocuous change in the future could break the derived class (since the relationship is not well defined). In addition, it muddies the business meaning of the derived class. For example, an order is not a vector, although an order may contain a vector of line items.

it seems to be referring to things like this:

class Order(dict):
    def __repr__(self):
        return """
Customer: {customer}
Address: {address}
        """.format(**self)

o = Order(customer = "Joe Customer", address = "123 Market St")