z3c.viewlet 1.0.0

Weight-Ordered Viewlet Manager

The viewlet manager in zope.viewlet does not implement a particular way of sorting the viewlets it represents. This was intentional, since the authors did not want to suggest a particular method of sorting viewlets. Over time, however, it turns out that sorting viewlets by a relative weight is very useful and sufficient for most situations.

>>> from z3c.viewlet import manager

Every viewlet displayed by a weight-ordered viewlet manager is expected to have a weight attribute that is an integer; it can also be a string that can be converted to an integer. If a viewlet does not have this attribute, a weight of zero is assumed.

The manager uses a helper function to extract the weight. So let’s create a dummy viewlet:

>>> class Viewlet(object):
...   pass

>>> viewlet = Viewlet()

Initially, there is no weight attribute, so the weight is zero.

>>> manager.getWeight(('viewlet', viewlet))
0

If the viewlet has a weight, …

>>> viewlet.weight = 1

… it is returned:

>>> manager.getWeight(('viewlet', viewlet))
1

As mentioned before, the weight can also be a string representation of an integer:

>>> viewlet.weight = '2'
>>> manager.getWeight(('viewlet', viewlet))
2

Let’s now check that the sorting works correctly for the manager:

>>> zero = Viewlet()

>>> one = Viewlet()
>>> one.weight = 1

>>> two = Viewlet()
>>> two.weight = '2'

>>> viewlets = manager.WeightOrderedViewletManager(None, None, None)
>>> viewlets.sort([ ('zero', zero), ('one', one), ('two', two) ])
[('zero', <Viewlet object at ...>),
 ('one', <Viewlet object at ...>),
 ('two', <Viewlet object at ...>)]