dm.zope.schema 1.0

'zope.schema' extensions

This package contains extensions for zope.schema.

Modules

verify

A companion to zope.interface.verify for the schema part of interfaces.

It contains the function verify_schema(iface, obj, context=None, check_declaration=True) which verifies that obj satisfies the schema part of interface iface. Schema fields need to get bound to a context before they can be validated. context specifies this context and defaults to obj. check_declaration checks that obj declares to privide iface.

schema

The main content is the mixin class SchemaConfigured. It supports configuration according the schema part of the interfaces implemented by the SchemaConfigured derived class.

Occasionally, function schemadict might be usefull. It extracts the schema part of an interface or interface specification as a dictionary.

The field Object is a replacement for zope.schema.Object. The latter lacks field information in validation errors (https://bugs.launchpad.net/zope.schema/+bug/620324) which makes identification of the affected fields unnecessarily difficult. Occasionally, one wants to suppress the check that a validated object explicitly declares to provide the interface. Object has the additional property check_declaration to control this (defaults to True).

Examples

Setup: It defines two schemas S1 and S2, an interface I and a class C deriving from SchemaConfigured implementing the schemas and the interface.

>>> from zope.interface import Interface, implements, providedBy
>>> from zope.schema import Int
>>>
>>> from dm.zope.schema.schema import SchemaConfigured, schemadict
>>> from dm.zope.schema.verify import verify_schema
>>>
>>> class S1(Interface): i1 = Int(default=0)
...
>>> class S2(Interface): i2 = Int(default=1)
...
>>> class I(Interface):
...   def method(): pass
...
>>> class C(SchemaConfigured):
...   implements(S1, S2, I)
...   def method(self): pass
...

C instances have attributes corresponding to the schema fields. If no arguments are given for the constructor, they get the field default as value. Provided (keyword!) arguments override the defaults.

>>> c = C()
>>> c.i1
0
>>> c.i2
1
>>> c = C(i1=5)
>>> c.i1
5

The constructor rejects keyword arguments not defined in the schema in order to quickly detect spelling errors. However, this hampers the use of super in the class hierarchy for the __init__ method. Maybe, future versions will provide a means to control this check.

>>> c = C(x=5)
Traceback (most recent call last):
  ...
TypeError: non schema keyword argument: x

If the field values are appropriate, C instances provide the schemas (as verified by verify_schema). Otherwise, verify_schema will raise an exception. This example should also the elementary use of verify_schema.

>>> verify_schema(S1, c)
>>> c.i1=None
>>> verify_schema(S1, c)
Traceback (most recent call last):
  ...
zope.schema.interfaces.WrongContainedType: [('i1', RequiredMissing())]