# Bugs Everywhere - a distributed bugtracker # Copyright (C) 2008-2009 W. Trevor King # # This program is free software; you can redistribute it and/or modify # it under the terms of the GNU General Public License as published by # the Free Software Foundation; either version 2 of the License, or # (at your option) any later version. # # This program is distributed in the hope that it will be useful, # but WITHOUT ANY WARRANTY; without even the implied warranty of # MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the # GNU General Public License for more details. # # You should have received a copy of the GNU General Public License along # with this program; if not, write to the Free Software Foundation, Inc., # 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301 USA. """ This module provides a series of useful decorators for defining various types of properties. For example usage, consider the unittests at the end of the module. See http://www.python.org/dev/peps/pep-0318/ and http://www.phyast.pitt.edu/~micheles/python/documentation.html for more information on decorators. """ import copy import types import unittest class ValueCheckError (ValueError): def __init__(self, name, value, allowed): action = "in" # some list of allowed values if type(allowed) == types.FunctionType: action = "allowed by" # some allowed-value check function msg = "%s not %s %s for %s" % (value, action, allowed, name) ValueError.__init__(self, msg) self.name = name self.value = value self.allowed = allowed def Property(funcs): """ End a chain of property decorators, returning a property. """ args = {} args["fget"] = funcs.get("fget", None) 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) def doc_property(doc=None): """ Add a docstring to a chain of property decorators. """ def decorator(funcs=None): """ Takes either a dict of funcs {"fget":fnX, "fset":fnY, ...} or a function fn() returning such a dict. """ if hasattr(funcs, "__call__"): funcs = funcs() # convert from function-arg to dict funcs["doc"] = doc return funcs return decorator def local_property(name, null=None, mutable_null=False): """ Define get/set access to per-parent-instance local storage. Uses .__value to store the value for a particular owner instance. If the .__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__"): funcs = funcs() fget = funcs.get("fget", None) fset = funcs.get("fset", None) def _fget(self): if fget is not None: fget(self) if mutable_null == True: ret_null = copy.deepcopy(null) else: ret_null = null value = getattr(self, "_%s_value" % name, ret_null) return value def _fset(self, value): setattr(self, "_%s_value" % name, value) if fset is not None: fset(self, value) funcs["fget"] = _fget funcs["fset"] = _fset funcs["name"] = name return funcs return decorator def settings_property(name, null=None): """ Similar to local_property, except where local_property stores the value in instance.__value, settings_property stores the value in instance.settings[name]. """ def decorator(funcs): if hasattr(funcs, "__call__"): funcs = funcs() fget = funcs.get("fget", None) fset = funcs.get("fset", None) def _fget(self): if fget is not None: fget(self) value = self.settings.get(name, null) return value def _fset(self, value): self.settings[name] = value if fset is not None: fset(self, value) funcs["fget"] = _fget funcs["fset"] = _fset funcs["name"] = name return funcs return decorator # Allow comparison and caching with _original_ values for mutables, # since # # >>> a = [] # >>> b = a # >>> b.append(1) # >>> a # [1] # >>> a==b # True def _hash_mutable_value(value): return repr(value) def _init_mutable_property_cache(self): if not hasattr(self, "_mutable_property_cache_hash"): # first call to _fget for any mutable property self._mutable_property_cache_hash = {} self._mutable_property_cache_copy = {} def _set_cached_mutable_property(self, cacher_name, property_name, value): _init_mutable_property_cache(self) self._mutable_property_cache_hash[(cacher_name, property_name)] = \ _hash_mutable_value(value) self._mutable_property_cache_copy[(cacher_name, property_name)] = \ copy.deepcopy(value) def _get_cached_mutable_property(self, cacher_name, property_name, default=None): _init_mutable_property_cache(self) if (cacher_name, property_name) not in self._mutable_property_cache_copy: return default return self._mutable_property_cache_copy[(cacher_name, property_name)] def _cmp_cached_mutable_property(self, cacher_name, property_name, value): _init_mutable_property_cache(self) if (cacher_name, property_name) not in self._mutable_property_cache_hash: return 1 # any value > non-existant old hash old_hash = self._mutable_property_cache_hash[(cacher_name, property_name)] return cmp(_hash_mutable_value(value), old_hash) def defaulting_property(default=None, null=None, 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__"): funcs = funcs() fget = funcs.get("fget") fset = funcs.get("fset") name = funcs.get("name", "") def _fget(self): value = fget(self) if value == null: if mutable_default == True: return copy.deepcopy(default) else: return default return value def _fset(self, value): if value == default: value = null fset(self, value) funcs["fget"] = _fget funcs["fset"] = _fset return funcs return decorator def fn_checked_property(value_allowed_fn): """ Define allowed values for get/set access to a property. """ def decorator(funcs): if hasattr(funcs, "__call__"): funcs = funcs() fget = funcs.get("fget") fset = funcs.get("fset") name = funcs.get("name", "") def _fget(self): value = fget(self) if value_allowed_fn(value) != True: raise ValueCheckError(name, value, value_allowed_fn) return value def _fset(self, value): if value_allowed_fn(value) != True: raise ValueCheckError(name, value, value_allowed_fn) fset(self, value) funcs["fget"] = _fget funcs["fset"] = _fset return funcs return decorator def checked_property(allowed=[]): """ Define allowed values for get/set access to a property. """ def decorator(funcs): if hasattr(funcs, "__call__"): funcs = funcs() fget = funcs.get("fget") fset = funcs.get("fset") name = funcs.get("name", "") def _fget(self): value = fget(self) if value not in allowed: raise ValueCheckError(name, value, allowed) return value def _fset(self, value): if value not in allowed: raise ValueCheckError(name, value, allowed) fset(self, value) funcs["fget"] = _fget funcs["fset"] = _fset return funcs return decorator def cached_property(generator, initVal=None, mutable=False): """ Allow caching of values generated by generator(instance), where instance is the instance to which this property belongs. Uses .__cache to store a cache flag for a particular owner instance. When the cache flag is True or missing and the stored value is initVal, the first fget call triggers the generator function, whose output is stored in __cached_value. That and subsequent calls to fget will return this cached value. 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. The cache flag is missing on initialization. Particular instances may override by setting their own flag. In the case that mutable == True, all caching is disabled and the generator is called whenever the cached value would otherwise be used. """ def decorator(funcs): if hasattr(funcs, "__call__"): funcs = funcs() fget = funcs.get("fget") name = funcs.get("name", "") def _fget(self): cache = getattr(self, "_%s_cache" % name, True) value = fget(self) if value == initVal: if cache == True and mutable == False: if hasattr(self, "_%s_cached_value" % name): value = getattr(self, "_%s_cached_value" % name) else: value = generator(self) setattr(self, "_%s_cached_value" % name, value) else: value = generator(self) return value funcs["fget"] = _fget return funcs return decorator def primed_property(primer, initVal=None): """ Just like a cached_property, except that instead of returning a new value and running fset to cache it, the primer performs some background manipulation (e.g. loads data into instance.settings) such that a _second_ pass through fget succeeds. The 'cache' flag becomes a 'prime' flag, with priming taking place whenever .__prime is True, or is False or missing and value == initVal. """ def decorator(funcs): if hasattr(funcs, "__call__"): funcs = funcs() fget = funcs.get("fget") name = funcs.get("name", "") def _fget(self): prime = getattr(self, "_%s_prime" % name, False) if prime == False: value = fget(self) if prime == True or (prime == False and value == initVal): primer(self) value = fget(self) return value funcs["fget"] = _fget return funcs return decorator def change_hook_property(hook, mutable=False): """ Call the function hook(instance, old_value, new_value) whenever a value different from the current value is set (instance is a a reference to the class instance to which this property belongs). This is useful for saving changes to disk, etc. This function is 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__"): funcs = funcs() fget = funcs.get("fget") fset = funcs.get("fset") name = funcs.get("name", "") def _fget(self, new_value=None, from_fset=False): # only used if mutable == True 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) _set_cached_mutable_property(self, "change hook property", name, value) if from_fset == True: # return previously cached value value = old_value else: # the value changed while we weren't looking hook(self, old_value, value) return value def _fset(self, value): if mutable == True: # get cached previous value old_value = _fget(self, new_value=value, from_fset=True) else: old_value = fget(self) fset(self, value) if value != old_value: hook(self, old_value, value) if mutable == True: funcs["fget"] = _fget funcs["fset"] = _fset return funcs return decorator class DecoratorTests(unittest.TestCase): def testLocalDoc(self): class Test(object): @Property @doc_property("A fancy property") def x(): return {} self.failUnless(Test.x.__doc__ == "A fancy property", Test.x.__doc__) def testLocalProperty(self): class Test(object): @Property @local_property(name="LOCAL") def x(): return {} t = Test() self.failUnless(t.x == None, str(t.x)) t.x = 'z' # the first set initializes ._LOCAL_value self.failUnless(t.x == 'z', str(t.x)) self.failUnless("_LOCAL_value" in dir(t), dir(t)) self.failUnless(t._LOCAL_value == 'z', t._LOCAL_value) def testSettingsProperty(self): class Test(object): @Property @settings_property(name="attr") def x(): return {} def __init__(self): self.settings = {} t = Test() self.failUnless(t.x == None, str(t.x)) t.x = 'z' # the first set initializes ._LOCAL_value self.failUnless(t.x == 'z', str(t.x)) self.failUnless("attr" in t.settings, t.settings) self.failUnless(t.settings["attr"] == 'z', t.settings["attr"]) def testDefaultingLocalProperty(self): class Test(object): @Property @defaulting_property(default='y', null='x') @local_property(name="DEFAULT", null=5) def x(): return {} t = Test() self.failUnless(t.x == 5, str(t.x)) t.x = 'x' self.failUnless(t.x == 'y', str(t.x)) t.x = 'y' self.failUnless(t.x == 'y', str(t.x)) t.x = 'z' self.failUnless(t.x == 'z', str(t.x)) t.x = 5 self.failUnless(t.x == 5, str(t.x)) def testCheckedLocalProperty(self): class Test(object): @Property @checked_property(allowed=['x', 'y', 'z']) @local_property(name="CHECKED") def x(): return {} def __init__(self): self._CHECKED_value = 'x' t = Test() self.failUnless(t.x == 'x', str(t.x)) try: t.x = None e = None except ValueCheckError, e: pass self.failUnless(type(e) == ValueCheckError, type(e)) def testTwoCheckedLocalProperties(self): class Test(object): @Property @checked_property(allowed=['x', 'y', 'z']) @local_property(name="X") def x(): return {} @Property @checked_property(allowed=['a', 'b', 'c']) @local_property(name="A") def a(): return {} def __init__(self): self._A_value = 'a' self._X_value = 'x' t = Test() try: t.x = 'a' e = None except ValueCheckError, e: pass self.failUnless(type(e) == ValueCheckError, type(e)) t.x = 'x' t.x = 'y' t.x = 'z' try: t.a = 'x' e = None except ValueCheckError, e: pass self.failUnless(type(e) == ValueCheckError, type(e)) t.a = 'a' t.a = 'b' t.a = 'c' def testFnCheckedLocalProperty(self): class Test(object): @Property @fn_checked_property(lambda v : v in ['x', 'y', 'z']) @local_property(name="CHECKED") def x(): return {} def __init__(self): self._CHECKED_value = 'x' t = Test() self.failUnless(t.x == 'x', str(t.x)) try: t.x = None e = None except ValueCheckError, e: pass self.failUnless(type(e) == ValueCheckError, type(e)) def testCachedLocalProperty(self): class Gen(object): def __init__(self): self.i = 0 def __call__(self, owner): self.i += 1 return self.i class Test(object): @Property @cached_property(generator=Gen(), initVal=None) @local_property(name="CACHED") def x(): return {} t = Test() self.failIf("_CACHED_cache" in dir(t), getattr(t, "_CACHED_cache", None)) self.failUnless(t.x == 1, t.x) self.failUnless(t.x == 1, t.x) self.failUnless(t.x == 1, t.x) t.x = 8 self.failUnless(t.x == 8, t.x) self.failUnless(t.x == 8, t.x) t._CACHED_cache = False # Caching is off, but the stored value val = t.x # is 8, not the initVal (None), so we self.failUnless(val == 8, val) # get 8. t._CACHED_value = None # Now we've set the stored value to None val = t.x # so future calls to fget (like this) self.failUnless(val == 2, val) # will call the generator every time... val = t.x self.failUnless(val == 3, val) val = t.x self.failUnless(val == 4, val) t._CACHED_cache = True # We turn caching back on, and get self.failUnless(t.x == 1, str(t.x)) # the original cached value. del t._CACHED_cached_value # Removing that value forces a self.failUnless(t.x == 5, str(t.x)) # single cache-regenerating call self.failUnless(t.x == 5, str(t.x)) # to the genenerator, after which self.failUnless(t.x == 5, str(t.x)) # we get the new cached value. def testPrimedLocalProperty(self): class Test(object): def prime(self): self.settings["PRIMED"] = "initialized" @Property @primed_property(primer=prime, initVal=None) @settings_property(name="PRIMED") def x(): return {} def __init__(self): self.settings={} t = Test() self.failIf("_PRIMED_prime" in dir(t), getattr(t, "_PRIMED_prime", None)) self.failUnless(t.x == "initialized", t.x) t.x = 1 self.failUnless(t.x == 1, t.x) t.x = None self.failUnless(t.x == "initialized", t.x) t._PRIMED_prime = True t.x = 3 self.failUnless(t.x == "initialized", t.x) t._PRIMED_prime = False t.x = 3 self.failUnless(t.x == 3, t.x) def testChangeHookLocalProperty(self): class Test(object): def _hook(self, old, new): self.old = old self.new = new @Property @change_hook_property(_hook) @local_property(name="HOOKED") def x(): return {} t = Test() t.x = 1 self.failUnless(t.old == None, t.old) self.failUnless(t.new == 1, t.new) t.x = 1 self.failUnless(t.old == None, t.old) self.failUnless(t.new == 1, t.new) t.x = 2 self.failUnless(t.old == 1, t.old) self.failUnless(t.new == 2, t.new) def testChangeHookMutableProperty(self): class Test(object): def _hook(self, old, new): self.old = old self.new = new self.hook_calls += 1 @Property @change_hook_property(_hook, mutable=True) @local_property(name="HOOKED") def x(): return {} t = Test() t.hook_calls = 0 t.x = [] self.failUnless(t.old == None, t.old) self.failUnless(t.new == [], t.new) a = t.x a.append(5) t.x = a self.failUnless(t.old == [], t.old) self.failUnless(t.new == [5], t.new) t.x = [] self.failUnless(t.old == [5], t.old) self.failUnless(t.new == [], t.new) # now append without reassigning. this doesn't trigger the # change, since we don't ever set t.x, only get it and mess # with it. It does, however, update our t.new, since t.new = # t.x and is not a static copy. t.x.append(5) self.failUnless(t.old == [5], t.old) self.failUnless(t.new == [5], t.new) # however, the next t.x get _will_ notice the change... a = t.x self.failUnless(t.old == [], t.old) self.failUnless(t.new == [5], t.new) self.failUnless(t.hook_calls == 6, t.hook_calls) t.x.append(6) # this append(6) is not noticed yet self.failUnless(t.old == [], t.old) self.failUnless(t.new == [5,6], t.new) self.failUnless(t.hook_calls == 6, t.hook_calls) # this append(7) is not noticed, but the t.x get causes the # append(6) to be noticed t.x.append(7) self.failUnless(t.old == [5], t.old) self.failUnless(t.new == [5,6,7], t.new) self.failUnless(t.hook_calls == 7, t.hook_calls) a = t.x # now the append(7) is noticed self.failUnless(t.old == [5,6], t.old) self.failUnless(t.new == [5,6,7], t.new) self.failUnless(t.hook_calls == 8, t.hook_calls) suite = unittest.TestLoader().loadTestsFromTestCase(DecoratorTests)