Zope

This package is intended to be independently reusable in any Python project and it is maintained by the Zope Toolkit project. This package provides an implementation of “object interfaces” for Python. Interfaces are a mechanism for labeling objects as conforming to a given API or contract.

So, this package can be considered as implementation of the Design By Contract methodology support in Python. Interfaces are objects that specify (document) the external behavior of objects that “provide” them. An interface specifies behavior through: Informal documentation in a doc string; Attribute definitions and; Invariants, which are conditions that must hold for objects that provide the interface.Attribute definitions specify specific attributes.

They define the attribute name and provide documentation and constraints of attribute values, and they can take a number of forms as listed below: Adapter registries provide a way to register objects that depend on one or more interface specifications and provide (perhaps indirectly) some interface. In addition, the registrations have names. The term “interface specification” refers both to interfaces and to interface declarations, such as declarations of interfaces implemented by a class.

This is a small demonstration of the zope.interface package including its adapter registry. It is intended to provide a concrete but narrow example on how to use interfaces and adapters outside of Zope 3.For now, the platform simply supports one attribute, the body, which contains the actual file contents:For statistical reasons, you should specify the size of a file. However, it would be clumsy to implement the size directly in the file object, since the size really represents meta-data.