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Diffstat (limited to 'libbe/properties.py')
| -rw-r--r-- | libbe/properties.py | 479 |
1 files changed, 479 insertions, 0 deletions
diff --git a/libbe/properties.py b/libbe/properties.py new file mode 100644 index 0000000..a8e89fb --- /dev/null +++ b/libbe/properties.py @@ -0,0 +1,479 @@ +# Bugs Everywhere - a distributed bugtracker +# Copyright (C) 2008 W. Trevor King <wking@drexel.edu> +# +# 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 3 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, see <http://www.gnu.org/licenses/>. + +""" +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 unittest + + +class ValueCheckError (ValueError): + def __init__(self, name, value, allowed): + msg = "%s not in %s for %s" % (value, 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): + """ + 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. + """ + 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 = getattr(self, "_%s_value" % name, 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._<name>_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 + +def defaulting_property(default=None, null=None): + """ + Define a default value for get access to a property. + If the stored value is null, then default is returned. + """ + def decorator(funcs): + if hasattr(funcs, "__call__"): + funcs = funcs() + fget = funcs.get("fget") + def _fget(self): + value = fget(self) + if value == null: + return default + return value + funcs["fget"] = _fget + 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", "<unknown>") + 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", "<unknown>") + 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): + """ + Allow caching of values generated by generator(instance), where + instance is the instance to which this property belongs. Uses + ._<name>_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, + whiose output is stored in _<name>_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. + """ + def decorator(funcs): + if hasattr(funcs, "__call__"): + funcs = funcs() + fget = funcs.get("fget") + fset = funcs.get("fset") + name = funcs.get("name", "<unknown>") + def _fget(self): + cache = getattr(self, "_%s_cache" % name, True) + value = fget(self) + if cache == True: + if value == initVal: + 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: + if value == initVal: + value = generator(self) + return value + funcs["fget"] = _fget + return funcs + return decorator + +def primed_property(primer, initVal=None): + """ + Just like a generator_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 ._<name>_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", "<unknown>") + 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): + """ + 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. + """ + def decorator(funcs): + if hasattr(funcs, "__call__"): + funcs = funcs() + fget = funcs.get("fget") + fset = funcs.get("fset") + name = funcs.get("name", "<unknown>") + def _fset(self, value): + old_value = fget(self) + if value != old_value: + hook(self, old_value, value) + fset(self, value) + 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") + def x(): return {} + t = Test() + self.failUnless(t.x == None, 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)) + 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) + +suite = unittest.TestLoader().loadTestsFromTestCase(DecoratorTests) + |