it is an enhanced property
* initialize attribute in class definition scope
* easily keep the attribute behaviors in sub classes.
* easy to define interface.
* not afraid to forget the super(klass, self).__init__(...) :P
Python, 312 lines
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Copy to clipboard1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60 61 62 63 64 65 66 67 68 69 70 71 72 73 74 75 76 77 78 79 80 81 82 83 84 85 86 87 88 89 90 91 92 93 94 95 96 97 98 99 100 101 102 103 104 105 106 107 108 109 110 111 112 113 114 115 116 117 118 119 120 121 122 123 124 125 126 127 128 129 130 131 132 133 134 135 136 137 138 139 140 141 142 143 144 145 146 147 148 149 150 151 152 153 154 155 156 157 158 159 160 161 162 163 164 165 166 167 168 169 170 171 172 173 174 175 176 177 178 179 180 181 182 183 184 185 186 187 188 189 190 191 192 193 194 195 196 197 198 199 200 201 202 203 204 205 206 207 208 209 210 211 212 213 214 215 216 217 218 219 220 221 222 223 224 225 226 227 228 229 230 231 232 233 234 235 236 237 238 239 240 241 242 243 244 245 246 247 248 249 250 251 252 253 254 255 256 257 258 259 260 261 262 263 264 265 266 267 268 269 270 271 272 273 274 275 276 277 278 279 280 281 282 283 284 285 286 287 288 289 290 291 292 293 294 295 296 297 298 299 300 301 302 303 304 305 306 307 308 309 310 311 312 | #!/usr/bin/env python
#
# Copyright 2010- Hui Zhang
# E-mail: hui.zh012@gmail.com
#
# Distributed under the terms of the GPL (GNU Public License)
#
# 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., 59 Temple Place, Suite 330, Boston, MA 02111-1307 USA
__all__ = ["Attribute", "attribute", ]
from weakref import ref
from functools import partial
class BaseAttribute(object):
"""
usage:
>>>class A(object):
val = Attriubte('val',
factory=int,
validator=lambda v: v in range(3,7),
onchanged=somfunc,
readonly=True,
otw=False,
... # for more please check the code
)
>>> a = A()
>>> print a.val
0
>>> a.val=1; print a.val
1
>>> del a.val; print a.val
0
notes:
'del a.val' does not delete the attr from instance.
it just clean the assigned value for this attr.
parameters:
* name :
the attr's name, default is ''
* readonly :
define if the attr could be assigned.
notes: readonly does not impact behavior of 'del a.val'
* delable :
define if the value could be deleted
* default :
the default value.
* factory, boundfactory
define the initializer for the attr.
-factory takes no parametor
-boundfactory would get the instance as the only parameter.
* validator, boundvalidator, skip_valid_err
validate the value assigned to the attr.
if validate failed,
- the value would not be assigned
- a exception would be raised if skip_valid_err is False.
The validation would not be applied for the value initialized by:
default, factory, boundfactory
* onchanged
define a hook while attr value changed.
the following 4 args would be given to the hook:
(instance, Attribute instance, old value, new value)
* otw
one time write.
e.g:
class A(object):
v = Attribute(otw=True)
class B(A):
def __init__(self, value):
self.v = value
b = B(99)
print b.v -> 99
b.v = 100 -> exception raised
[initialization:]
initializers are prioritized as "default, factory, boundfactory"
if no any defined and value assinged, a exception would be raised while you try to read this attr.
"""
undefined = object()
def __init__(self, name='', **kwargs):
self.name = name
self.dict = kwargs.copy()
self.skip_valid_err = self.getarg('skip_valid_err', True)
self.build_initer()
self.build_assigner()
self.build_deleter()
onchanged = self.getarg('onchanged', None)
if onchanged:
self.onchanged(onchanged)
## read, write and erase the value from/to the storage
## to be implemented by sub classes
def _read_(self, instance):
""" read the value from the storage
raise exception if the value is not initialized
"""
def _write_(self, instance, value):
""" store the value to the storage
"""
def _earase_(self, instance):
""" erase the value from the storage
"""
def __get__(self, instance, owner):
if instance is None:
return self
else:
try:
return self._read_(instance)
except:
if self.initer:
self._write_(instance, self.initer(instance))
return self._read_(instance)
raise AttributeError("Attribute is used before initialized.")
def __set__(self, instance, value):
self.assigner(instance, value)
def __delete__(self, instance):
self.deleter(instance)
## build the initer, assigner and deleter
def getarg(self, name, default):
if name in self.dict:
return self.dict.pop(name)
else:
return default
def build_initer(self):
self.initer = None
_dummy = object
default = self.getarg('default', _dummy)
if default is not _dummy:
self.initer = lambda instance: default
return
factory = self.getarg('factory', _dummy)
if factory is not _dummy:
self.initer = lambda instance: factory()
return
boundfactory = self.getarg('boundfactory', _dummy)
if boundfactory is not _dummy:
self.initer = lambda instance: boundfactory(instance)
return
def build_assigner(self):
readonly = self.getarg('readonly', False)
if readonly:
def assigner(instance, value):
raise AttributeError("Cannot set value to read-only attribute")
self.assigner = assigner
return
self.assigner = self._write_
otw = self.getarg('otw', False)
if otw:
self.set_otw()
validator = self.getarg('validator', None)
if validator:
self.validator(validator)
boundvalidator = self.getarg('boundvalidator', None)
if boundvalidator:
self.boundvalidator(boundvalidator)
def build_deleter(self):
delable = self.getarg('delable', True)
if not delable:
def deleter(instance):
raise AttributeError("Cannot delete attribute")
self.deleter = deleter
else:
self.deleter = self._earase_
## handler wrappers
def set_otw(self):
oldassinger = self.assigner
def assigner(instance, value):
try:
self._read_(instance)
inited = True
except:
inited = False
if inited:
raise AttributeError('Attribute could only be written once.')
oldassinger(instance, value)
self.assigner = assigner
# be able to use as decorator
def onchanged(self, hook):
def wrap(func):
def newfunc(*args):
instance = args[0]
try:
oldval = self.__get__(instance, None)
except:
oldval = BaseAttribute.undefined
func(*args)
try:
newval = self.__get__(instance, None)
except:
newval = BaseAttribute.undefined
if oldval != newval:
hook(instance, self, oldval, newval)
return newfunc
self.assigner = wrap(self.assigner)
self.deleter = wrap(self.deleter)
return self
def validator(self, hook):
oldassinger = self.assigner
def assigner(instance, value):
if hook(value):
oldassinger(instance, value)
elif not self.skip_valid_err:
raise AttributeError("The value for attribute is not valid")
self.assigner = assigner
return self
def boundvalidator(self, hook):
oldassinger = self.assigner
def assigner(instance, value):
if hook(instance, value):
oldassinger(instance, value)
elif not self.skip_valid_err:
raise AttributeError("The value for attribute is not valid")
self.assigner = assigner
return self
class Attribute(BaseAttribute):
def __init__(self, name='', **kwargs):
super(Attribute, self).__init__(name, **kwargs)
self.__values = weakkeymap() # Recipe 577580: weak reference map
def _read_(self, instance):
return self.__values.get(instance)
def _write_(self, instance, value):
self.__values.set(instance, value)
def _earase_(self, instance):
self.__values.remove(instance)
def attribute(*args, **kwargs):
assert 'boundfactory' not in kwargs \
and ( not args
or (len(args)==1 and not kwargs)
)
if args:
return Attribute(args[0].func_name,
boundfactory=args[0])
else:
def deco(func):
return Attribute(func.func_name,
boundfactory=func,
**kwargs)
return deco
## demo code
#class A(object):
# @attribute(skip_valid_err=False)
# def value(self):
# return 10000
#
# @value.boundvalidator
# def value(self, v):
# return v < 20
#
# value.validator(lambda v: v>5)
#
# @value.onchanged
# def value(self, *args):
# print args
#
#a = A()
#print a.value
#a.value = 9
#print a.value
#a.value = 100
|
s/Attriubte/Attribute/