/usr/share/pyshared/zope/minmax/minmax.txt is in python-zope.minmax 1.1.2-0ubuntu5.
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Conflict Resolution using Maximum or Minimum Values
===================================================
The `zope.minmax.AbstractValue` class provides a super class which can
be subclassed to store arbitrary *homogeneous* values in a persistent
storage and apply different conflict resolution policies.
The subclasses defined here are resolving the conflicts using always
either the maximum or the minimum of the conflicting values.
Maximum
-------
The `zope.minmax.Maximum` class always resolves conflicts favoring the
maximum value. Let's instantiate one object and verify that it
satisfies the interface.
>>> import zope.minmax
>>> import zope.interface.verify
>>> max_favored = zope.minmax.Maximum()
>>> zope.interface.verify.verifyObject(
... zope.minmax.interfaces.IAbstractValue, max_favored)
True
We can confirm that the initial value is zero.
>>> bool(max_favored)
False
>>> print max_favored.value
None
Now, we can store a new value in the object.
>>> max_favored.value = 11
>>> print max_favored.value
11
>>> bool(max_favored)
True
Or we can use the methods.
>>> max_favored.__setstate__(4532)
>>> max_favored.__getstate__()
4532
>>> print max_favored.value
4532
>>> bool(max_favored)
True
Do notice that using a direct assignment to the value attribute is a
more natural use.
Minimum
-------
The `zope.minmax.Minimum` class always resolves conflicts favoring the
minimum value. Again, we instantiate an object and verify that it
satisfies the interface.
>>> min_favored = zope.minmax.Minimum()
>>> zope.interface.verify.verifyObject(
... zope.minmax.interfaces.IAbstractValue, min_favored)
True
We need a confirmation that the initial value is zero.
>>> bool(min_favored)
False
>>> print min_favored.value
None
Let's populate this one too.
>>> min_favored.value = 22
>>> print min_favored.value
22
>>> bool(min_favored)
True
Or we can use the methods, again.
>>> min_favored.__setstate__(8796)
>>> min_favored.__getstate__()
8796
>>> print min_favored.value
8796
>>> bool(min_favored)
True
Please, notice, again, that using a direct assignment to the value
attribute is a more natural use.
Conflict Resolution
-------------------
Now, we need to exercise the conflict resolution interface.
First for the `zope.minmax.Maximum`:
Let's try differing values larger than the old value.
>>> max_favored._p_resolveConflict(max_favored.value, 4536, 4535)
4536
>>> max_favored._p_resolveConflict(max_favored.value, 4573, 4574)
4574
What happens when all the values are equal, including the old.
>>> max_favored._p_resolveConflict(max_favored.value, 4532, 4532)
4532
Notice that when the old value is larger than both the committed and
new, it is still disregarded.
>>> max_favored._p_resolveConflict(max_favored.value, 4531, 4530)
4531
Now, the `zope.minmax.Minimum`:
Let's try differing values smaller than the old value.
>>> min_favored._p_resolveConflict(min_favored.value, 8792, 8791)
8791
>>> min_favored._p_resolveConflict(min_favored.value, 8785, 8786)
8785
What happens when all the values are equal, including the old.
>>> min_favored._p_resolveConflict(min_favored.value, 8796, 8796)
8796
Notice that when the old value is smaller than both the committed and
new, it is still disregarded.
>>> min_favored._p_resolveConflict(min_favored.value, 8798, 8799)
8798
How about an example that is not numerical?
>>> max_word = zope.minmax.Maximum('joy')
>>> print max_word.value
joy
>>> bool(max_word)
True
>>> max_word._p_resolveConflict(max_word.value, 'happiness', 'exuberance')
'happiness'
>>> max_word._p_resolveConflict(max_word.value, 'exuberance', 'happiness')
'happiness'
>>> min_word = zope.minmax.Minimum(max_word.value)
>>> print min_word.value
joy
>>> bool(min_word)
True
>>> min_word._p_resolveConflict(min_word.value, 'happiness', 'exuberance')
'exuberance'
>>> min_word._p_resolveConflict(min_word.value, 'exuberance', 'happiness')
'exuberance'
As indicated, we don't need to have numbers, just *homegeneous* items.
The homogeneous values are not really inherently required. However, it
makes no sense to apply min() or max() on, say, one number and one
string. Simply, the ordering relations do not work at all on
heterogeneous values.
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