python-zope.schema - 4.4.2-3 main

Schemas extend the notion of interfaces to detailed descriptions of
Attributes (but not methods). Every schema is an interface and
specifies the public fields of an object. A *field* roughly
corresponds to an attribute of a Python object. But a Field provides
space for at least a title and a description. It can also constrain
its value and provide a validation method. Besides you can optionally
specify characteristics such as its value being read-only or not
required.
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This is the Python 2 version.