zc.freeze 1.0

Conveniences

The package does provide two default implementations of IFreezing, and a few conveniences.

One IFreezing implementation is for objects that are directly aware of this API (as opposed to having the functionality assembled from adapters and other components).

>>> import zc.freeze
>>> v = zc.freeze.Freezing()
>>> from zc.freeze import interfaces
>>> from zope.interface.verify import verifyObject
>>> verifyObject(interfaces.IFreezing, v)
True
>>> verifyObject(interfaces.IFreezable, v)
True
>>> v._z_frozen
False
>>> v._z_frozen = True
Traceback (most recent call last):
...
AttributeError: can't set attribute
>>> import pytz
>>> import datetime
>>> before = datetime.datetime.now(pytz.utc)
>>> v._z_freeze()
>>> before <= v._z_freeze_timestamp <= datetime.datetime.now(pytz.utc)
True
>>> v._z_frozen
True
>>> interfaces.IObjectFrozenEvent.providedBy(events[-1])
True
>>> events[-1].object is v
True
>>> v._z_freeze()
Traceback (most recent call last):
...
FrozenError

Another available implementation is an adapter, and stores the information in an annotation. Here’s a quick demo.

>>> import zope.annotation.interfaces
>>> from zope import interface, component
>>> class Demo(object):
...     interface.implements(zope.annotation.interfaces.IAnnotatable)
...
>>> import UserDict
>>> class DemoAnnotations(UserDict.UserDict):
...     interface.implements(zope.annotation.interfaces.IAnnotations)
...     component.adapts(Demo)
...     def __init__(self, context):
...         self.context = context
...         self.data = getattr(context, '_z_demo', None)
...         if self.data is None:
...             self.data = context._z_demo = {}
...
>>> component.provideAdapter(DemoAnnotations)
>>> component.provideAdapter(zc.freeze.FreezingAdapter)
>>> d = Demo()
>>> verifyObject(interfaces.IFreezing, interfaces.IFreezing(d))
True
>>> verifyObject(interfaces.IFreezable, interfaces.IFreezing(d))
True
>>> interfaces.IFreezing(d)._z_frozen
False
>>> interfaces.IFreezing(d)._z_frozen = True
Traceback (most recent call last):
...
AttributeError: can't set attribute
>>> before = datetime.datetime.now(pytz.utc)
>>> interfaces.IFreezing(d)._z_freeze()
>>> (before <= interfaces.IFreezing(d)._z_freeze_timestamp <=
...  datetime.datetime.now(pytz.utc))
True
>>> interfaces.IFreezing(d)._z_frozen
True
>>> interfaces.IObjectFrozenEvent.providedBy(events[-1])
True
>>> events[-1].object is d
True
>>> interfaces.IFreezing(d)._z_freeze()
Traceback (most recent call last):
...
FrozenError

The zc.freeze module also contains three helpers for writing properties and methods that are freeze-aware.

A ‘method’ function can generate a freeze-aware method that raises a FrozenError if the object has been frozen.

‘setproperty’ and ‘delproperty’ functions can generate a freeze-aware descriptor that raises a FrozenError if the set or del methods are called on a frozen object. These are rwproperties (see rwproperty.txt; imported from another project.)

‘makeProperty’ generates a freeze-aware descriptor that does a simple get/set but raises FrozenError if the set is attempted on a frozen object.

>>> class BiggerDemo(Demo):
...     counter = 0
...     @zc.freeze.method
...     def increase(self):
...         self.counter += 1
...     _complex = 1
...     @property
...     def complex_property(self):
...         return str(self._complex)
...     @zc.freeze.setproperty
...     def complex_property(self, value):
...         self._complex = value * 2
...     zc.freeze.makeProperty('simple_property')
...
>>> d = BiggerDemo()
>>> d.counter
0
>>> d.complex_property
'1'
>>> d.simple_property # None
>>> d.increase()
>>> d.counter
1
>>> d.complex_property = 4
>>> d.complex_property
'8'
>>> d.simple_property = 'hi'
>>> d.simple_property
'hi'
>>> interfaces.IFreezing(d)._z_frozen
False
>>> interfaces.IFreezing(d)._z_freeze()
>>> interfaces.IFreezing(d)._z_frozen
True
>>> d.counter
1
>>> d.increase()
Traceback (most recent call last):
...
FrozenError
>>> d.counter
1
>>> d.complex_property
'8'
>>> d.complex_property = 10
Traceback (most recent call last):
...
FrozenError
>>> d.complex_property
'8'
>>> d.simple_property
'hi'
>>> d.simple_property = 'bye'
Traceback (most recent call last):
...
FrozenError
>>> d.simple_property
'hi'