diff options
Diffstat (limited to 'libbe/properties.py')
| -rw-r--r-- | libbe/properties.py | 45 |
1 files changed, 32 insertions, 13 deletions
diff --git a/libbe/properties.py b/libbe/properties.py index 8c039b2..02504e0 100644 --- a/libbe/properties.py +++ b/libbe/properties.py @@ -52,7 +52,7 @@ def Property(funcs): args["fset"] = funcs.get("fset", None) args["fdel"] = funcs.get("fdel", None) args["doc"] = funcs.get("doc", None) - + #print "Creating a property with" #for key, val in args.items(): print key, value return property(**args) @@ -77,6 +77,9 @@ def local_property(name, null=None, mutable_null=False): Define get/set access to per-parent-instance local storage. Uses ._<name>_value to store the value for a particular owner instance. If the ._<name>_value attribute does not exist, returns null. + + If mutable_null == True, we only release deepcopies of the null to + the outside world. """ def decorator(funcs): if hasattr(funcs, "__call__"): @@ -166,11 +169,16 @@ def _cmp_cached_mutable_property(self, cacher_name, property_name, value): def defaulting_property(default=None, null=None, - default_mutable=False, - null_mutable=False): + mutable_default=False): """ Define a default value for get access to a property. If the stored value is null, then default is returned. + + If mutable_default == True, we only release deepcopies of the + default to the outside world. + + null should never escape to the outside world, so don't worry + about it being a mutable. """ def decorator(funcs): if hasattr(funcs, "__call__"): @@ -181,17 +189,14 @@ def defaulting_property(default=None, null=None, def _fget(self): value = fget(self) if value == null: - if default_mutable == True: + if mutable_default == True: return copy.deepcopy(default) else: return default return value def _fset(self, value): if value == default: - if null_mutable == True: - value = copy.deepcopy(null) - else: - value = null + value = null fset(self, value) funcs["fget"] = _fget funcs["fset"] = _fset @@ -261,7 +266,7 @@ def cached_property(generator, initVal=None, mutable=False): If the input value is no longer initVal (e.g. a value has been loaded from disk or set with fset), that value overrides any cached value, and this property has no effect. - + When the cache flag is False and the stored value is initVal, the generator is not cached, but is called on every fget. @@ -270,7 +275,7 @@ def cached_property(generator, initVal=None, mutable=False): In the case that mutable == True, all caching is disabled and the generator is called whenever the cached value would otherwise be - used. This avoids uncertainties in the value of stored mutables. + used. """ def decorator(funcs): if hasattr(funcs, "__call__"): @@ -331,6 +336,17 @@ def change_hook_property(hook, mutable=False): called _after_ the new value has been stored, allowing you to change the stored value if you want. + In the case of mutables, things are slightly trickier. Because + the property-owning class has no way of knowing when the value + changes. We work around this by caching a private deepcopy of the + mutable value, and checking for changes whenever the property is + set (obviously) or retrieved (to check for external changes). So + long as you're conscientious about accessing the property after + making external modifications, mutability woln't be a problem. + t.x.append(5) # external modification + t.x # dummy access notices change and triggers hook + See testChangeHookMutableProperty for an example of the expected + behavior. """ def decorator(funcs): if hasattr(funcs, "__call__"): @@ -339,7 +355,10 @@ def change_hook_property(hook, mutable=False): fset = funcs.get("fset") name = funcs.get("name", "<unknown>") def _fget(self, new_value=None, from_fset=False): # only used if mutable == True - value = fget(self) + if from_fset == True: + value = new_value # compare new value with cached + else: + value = fget(self) # compare current value with cached if _cmp_cached_mutable_property(self, "change hook property", name, value) != 0: # there has been a change, cache new value old_value = _get_cached_mutable_property(self, "change hook property", name) @@ -362,7 +381,7 @@ def change_hook_property(hook, mutable=False): funcs["fset"] = _fset return funcs return decorator - + class DecoratorTests(unittest.TestCase): def testLocalDoc(self): @@ -406,7 +425,7 @@ class DecoratorTests(unittest.TestCase): @local_property(name="DEFAULT", null=5) def x(): return {} t = Test() - self.failUnless(t.x == 5, str(t.x)) + self.failUnless(t.x == 5, str(t.x)) t.x = 'x' self.failUnless(t.x == 'y', str(t.x)) t.x = 'y' |