openstack/deb-python-colander
Code Issues Proposed changes

explain inheritance rules

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This commit is contained in:
Chris McDonough
2012-10-09 02:59:50 -04:00
parent eba97d15fc
commit 718ba03cbb
1 changed files with 115 additions and 5 deletions
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120
CHANGES.txt
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@@ -82,11 +82,6 @@ Features
``self``, and it needs to support callables that are not methods, so it
sends ``node`` in regardless.
Normal inheritance rules apply to class attributes and methods defined in
a schemanode subclass. If your schemanode subclass inherits from another
schemanode class, your schemanode subclass' methods and class attributes
will override the superclass' methods and class attributes.
You can't currently use *method* definitions as ``colander.deferred``
callables. For example this will *not* work::
@@ -218,6 +213,121 @@ Features
``title`` attribute will be ``Some Schema`` (schema.title will return
``Some Schema``).
Normal inheritance rules apply to class attributes and methods defined in
a schemanode subclass. If your schemanode subclass inherits from another
schemanode class, your schemanode subclass' methods and class attributes
will override the superclass' methods and class attributes.
Ordering of child schema nodes when inheritance is used works like this:
the "deepest" SchemaNode class in the MRO of the inheritance chain is
consulted first for nodes, then the next deepest, then the next, and so
on. So the deepest class' nodes come first in the relative ordering of
schema nodes, then the next deepest, and so on. For example::
class One(colander.Schema):
a = colander.SchemaNode(
colander.String(),
id='a1',
)
b = colander.SchemaNode(
colander.String(),
id='b1',
)
d = colander.SchemaNode(
colander.String(),
id='d1',
)
class Two(One):
a = colander.SchemaNode(
colander.String(),
id='a2',
)
c = colander.SchemaNode(
colander.String(),
id='c2',
)
e = colander.SchemaNode(
colander.String(),
id='e2',
)
class Three(Two):
b = colander.SchemaNode(
colander.String(),
id='b3',
)
d = colander.SchemaNode(
colander.String(),
id='d3',
)
f = colander.SchemaNode(
colander.String(),
id='f3',
)
three = Three()
The ordering of child nodes computed in the schema node ``three`` will be
``['a2', 'b3', 'd3', 'c2', 'e2', 'f3']``. The ordering starts ``a1``,
``b1``, ``d1`` because that's the ordering of nodes in ``One``, and
``One`` is the deepest SchemaNode in the inheritance hierarchy. Then it
processes the nodes attached to ``Two``, the next deepest, which causes
``a1`` to be replaced by ``a2``, and ``c2`` and ``e2`` to be appended to
the node list. Then finally it processes the nodes attached to ``Three``,
which causes ``b1`` to be replaced by ``b3``, and ``d1`` to be replaced by
``d3``, then finally ``f`` is appended.
Multiple inheritance works the same way::
class One(colander.Schema):
a = colander.SchemaNode(
colander.String(),
id='a1',
)
b = colander.SchemaNode(
colander.String(),
id='b1',
)
d = colander.SchemaNode(
colander.String(),
id='d1',
)
class Two(colander.Schema):
a = colander.SchemaNode(
colander.String(),
id='a2',
)
c = colander.SchemaNode(
colander.String(),
id='c2',
)
e = colander.SchemaNode(
colander.String(),
id='e2',
)
class Three(Two, One):
b = colander.SchemaNode(
colander.String(),
id='b3',
)
d = colander.SchemaNode(
colander.String(),
id='d3',
)
f = colander.SchemaNode(
colander.String(),
id='f3',
)
three = Three()
The resulting node ordering of ``three`` is the same as the single
inheritance example: ``['a2', 'b3', 'd3', 'c2', 'e2', 'f3']`` due to the
MRO deepest-first ordering (``One``, then ``Two``, then ``Three``).
Backwards Incompatibilities
~~~~~~~~~~~~~~~~~~~~~~~~~~~