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14349.1.4
by Gavin Panella
Update copyright. |
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# Copyright 2010-2011 Canonical Ltd. This software is licensed under the
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11382.6.1
by Gavin Panella
New module propertycache, intended as a replacement for cachedproperty but with a cleaner API. |
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# GNU Affero General Public License version 3 (see the file LICENSE).
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11382.6.20
by Gavin Panella
Move propertycache documentation into a separate file. |
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"""
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Cached properties for situations where a property is computed once and then
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returned each time it is asked for.
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See `doc/propertycache.txt` for documentation.
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11382.6.1
by Gavin Panella
New module propertycache, intended as a replacement for cachedproperty but with a cleaner API. |
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"""
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__metaclass__ = type |
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__all__ = [ |
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11789.2.1
by Gavin Panella
Remove the need for adapters in propertycache. |
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'cachedproperty', |
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'clear_property_cache', |
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'get_property_cache', |
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11382.6.1
by Gavin Panella
New module propertycache, intended as a replacement for cachedproperty but with a cleaner API. |
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]
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from functools import partial |
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11382.6.19
by Gavin Panella
Reformat imports. |
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from zope.interface import ( |
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implements, |
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Interface, |
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)
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11382.6.13
by Gavin Panella
Remove security proxies when getting the default property cache. |
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from zope.security.proxy import removeSecurityProxy |
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11382.6.1
by Gavin Panella
New module propertycache, intended as a replacement for cachedproperty but with a cleaner API. |
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class IPropertyCache(Interface): |
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def __getattr__(name): |
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"""Return the cached value corresponding to `name`.
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Raise `AttributeError` if no value is cached.
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"""
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def __setattr__(name, value): |
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"""Cache `value` for `name`."""
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def __delattr__(name): |
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"""Delete value for `name`.
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If no value is cached for `name` this is a no-op.
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"""
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def __contains__(name): |
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"""Whether or not `name` is cached."""
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def __iter__(): |
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"""Iterate over the cached names."""
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class DefaultPropertyCache: |
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"""A simple cache."""
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implements(IPropertyCache) |
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11382.6.23
by Gavin Panella
Explain why DefaultPropertyCache does not implement __getattr__ or __setattr__. |
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# __getattr__ -- well, __getattribute__ -- and __setattr__ are inherited
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# from object.
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11382.6.1
by Gavin Panella
New module propertycache, intended as a replacement for cachedproperty but with a cleaner API. |
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def __delattr__(self, name): |
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"""See `IPropertyCache`."""
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self.__dict__.pop(name, None) |
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def __contains__(self, name): |
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"""See `IPropertyCache`."""
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return name in self.__dict__ |
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def __iter__(self): |
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"""See `IPropertyCache`."""
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return iter(self.__dict__) |
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11789.2.2
by Gavin Panella
Remove all adaptors. |
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def get_property_cache(target): |
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"""Obtain a `DefaultPropertyCache` for any object."""
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if IPropertyCache.providedBy(target): |
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return target |
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else: |
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naked_target = removeSecurityProxy(target) |
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try: |
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return naked_target._property_cache |
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except AttributeError: |
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naked_target._property_cache = DefaultPropertyCache() |
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return naked_target._property_cache |
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def clear_property_cache(target): |
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"""Clear the property cache."""
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get_property_cache(target).__dict__.clear() |
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11382.6.40
by Gavin Panella
Register propertycache adapters with the global site manager so they're always available. |
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11382.6.1
by Gavin Panella
New module propertycache, intended as a replacement for cachedproperty but with a cleaner API. |
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class CachedProperty: |
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"""Cached property descriptor.
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Provides only the `__get__` part of the descriptor protocol. Setting and
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clearing cached values should be done explicitly via `IPropertyCache`
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instances.
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"""
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def __init__(self, populate, name): |
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"""Initialize this instance.
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`populate` is a callable responsible for providing the value when this
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property has not yet been cached.
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`name` is the name under which this property will cache itself.
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"""
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self.populate = populate |
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self.name = name |
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def __get__(self, instance, cls): |
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if instance is None: |
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return self |
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11789.2.2
by Gavin Panella
Remove all adaptors. |
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cache = get_property_cache(instance) |
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11382.6.1
by Gavin Panella
New module propertycache, intended as a replacement for cachedproperty but with a cleaner API. |
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try: |
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return getattr(cache, self.name) |
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except AttributeError: |
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value = self.populate(instance) |
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setattr(cache, self.name, value) |
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return value |
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14349.1.1
by Gavin Panella
Prevent set/delete operations on cached properties. |
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def __set__(self, instance, value): |
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raise AttributeError( |
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"%s cannot be set here; instead set explicitly with " |
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"get_property_cache(object).%s = %r" % ( |
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self.name, self.name, value)) |
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def __delete__(self, instance): |
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raise AttributeError( |
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"%s cannot be deleted here; instead delete explicitly " |
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"with del get_property_cache(object).%s" % ( |
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self.name, self.name)) |
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11382.6.1
by Gavin Panella
New module propertycache, intended as a replacement for cachedproperty but with a cleaner API. |
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def cachedproperty(name_or_function): |
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"""Decorator to create a cached property.
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11382.6.20
by Gavin Panella
Move propertycache documentation into a separate file. |
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See `doc/propertycache.txt` for usage.
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11382.6.1
by Gavin Panella
New module propertycache, intended as a replacement for cachedproperty but with a cleaner API. |
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"""
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if isinstance(name_or_function, basestring): |
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name = name_or_function |
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return partial(CachedProperty, name=name) |
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else: |
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name = name_or_function.__name__ |
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populate = name_or_function |
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return CachedProperty(name=name, populate=populate) |