# Bugs Everywhere - a distributed bugtracker
# Copyright (C) 2008-2009 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 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
._<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__"):
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._<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
# 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", "<unknown>")
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", "<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, mutable=False):
"""
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,
whose 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.
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", "<unknown>")
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 ._<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, 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", "<unknown>")
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)
self.failUnless(t.hook_calls == 1, t.hook_calls)
a = t.x
a.append(5)
t.x = a
self.failUnless(t.old == [], t.old)
self.failUnless(t.new == [5], t.new)
self.failUnless(t.hook_calls == 2, t.hook_calls)
t.x = []
self.failUnless(t.old == [5], t.old)
self.failUnless(t.new == [], t.new)
self.failUnless(t.hook_calls == 3, t.hook_calls)
# 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)
self.failUnless(t.hook_calls == 3, t.hook_calls)
# 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 == 4, 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 == 4, 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 == 5, 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 == 6, t.hook_calls)
suite = unittest.TestLoader().loadTestsFromTestCase(DecoratorTests)
