I define a 'Component' as an attribute (typing optional) that instances can assign objects to. Nothing special there, but their usefulness comes in with 'Abilities'. If a class inherits from 'ClassWithAbilities', it will be given a special attribute 'abilities' that will grow/shrink when other classes with abilities are assigned to an instances attributes. It increases/decreases the functionality of the instance depending on what objects are assigned to it. All of these abilities are accessed through the 'abilities' attribute. This is a redesign of Recipe 576852, but I believe is different enough to warrant a new recipe.
1 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 | # used for filtering out 'builtin' methods upon dir() of custom class
std_class_methods = dir(object)
std_instance_methods = dir(object())
# ------------- Components -------------------------------
class _ComponentAccessor(object):
def __init__(self):
# flags to prevent infinite recursion during obj '__get__'
self._breaks = {}
def __get__(self, instance, owner):
# if an 'instance' is passed
# return dict of {component attr: component value}
# else use 'owner'
# return dict of {component attr: component obj}
if instance is None:
obj = owner
else:
obj = instance
if self._get_break(obj):
return None
self._set_break(obj)
_d = {}
attrs = [a for a in dir(owner) if a not in std_class_methods]
for attr in attrs:
component = getattr(owner, attr)
if getattr(component, '_is_component', False):
_d[attr] = getattr(obj, attr)
self._release_break(obj)
return _d
def __set__(self, instance, value):
raise ValueError("Cannot change a '_ComponentAccessor'")
def __delete__(self, instance, value):
raise ValueError("Cannot delete a '_ComponentAccessor'")
def _get_break(self, obj):
return self._breaks.get(id(obj), False)
def _set_break(self, obj):
self._breaks[id(obj)] = True
def _release_break(self, obj):
self._breaks[id(obj)] = False
class ClassWithComponents(object):
""" inherit from this to provide component introspection """
# introspection flag
_utilizes_components = True
# introspection 'property' (read only) that will return
# the class' current Components
components = _ComponentAccessor()
class Component(object):
""" the data descriptor to add to a class """
_is_component = True
def __init__(self, type=None):
""" type - verify component is set to an instance
of 'type' when assigned
"""
self._type = type
self._cache = {} # TODO: make into weakref dict
def __get__(self, instance, owner):
if instance is None:
return self
return self._cache.get(id(instance), None)
def __set__(self, instance, value):
# check value against self._type
if value is not None:
if self._type is not None and not isinstance(value, self._type):
raise TypeError("Invalid type '%s' for component! Needs to be '%s'" %\
(value.__class__.__name__, self._type.__name__,))
self._cache[id(instance)] = value
def __delete__(self, instance):
del(self._cache[id(instance)])
# ------------- /Components ------------------------------
# ------------- Abilities --------------------------------
class _Ability(object):
def __init__(self, method_name, *bound_methods):
self.name = method_name
# TODO: could look at method # of args, etc...
self._methods = []
for bm in bound_methods:
self.append(bm)
def __str__(self):
return self.name
def __call__(self, *args, **kwargs):
if len(self._methods) == 0:
return None
elif len(self._methods) == 1:
# only 1 method, return its return value
return self._methods[0](*args, **kwargs)
else:
# call all of our methods in order, no return value
for m in self._methods:
m(*args, **kwargs)
def __add__(self, other):
if not isinstance(other, _Ability):
raise TypeError("Can only add _Abilities together!")
if other.name != self.name:
raise ValueError("Abilities have mismatched names!")
meth_list = self._methods + other._methods
return _Ability(self.name, *meth_list)
def append(self, bound_method):
if bound_method in self._methods:
raise ValueError("Cannot add duplicate methods to ability!")
self._methods.append(bound_method)
class _AbilityAccessor(tuple):
""" placeholder object for ability methods """
def __new__(cls, abilities=None):
if abilities is None:
abilities = []
# check for duplicate ability.names combine them
_ab_d = {}
for abil in abilities:
if abil.name not in _ab_d:
_ab_d[abil.name] = []
_ab_d[abil.name].append(abil)
abilities = []
for name, ab_list in _ab_d.items():
abil = ab_list.pop(0)
for ab in ab_list:
abil += ab
abilities.append(abil)
return tuple.__new__(cls, abilities)
def __init__(self, abilities=None):
tuple.__init__(self)
# create a method on self to pass call onto ability
# ignore passed in 'abilities' arg, use self
for ab in self:
object.__setattr__(self, ab.name, ab)
def __add__(self, other):
if isinstance(other, _AbilityAccessor):
abs = tuple.__add__(self, other)
elif isinstance(other, _Ability):
abs = []
abs.extend(self)
abs.append(other)
else:
raise TypeError("Can only add to other _AbilityAccessors!")
return _AbilityAccessor(abs)
class _AbilityLookup(object):
def __init__(self):
# dict of flags to prevent infinite recursion during '__get__'
self._breaks = {} # id(obj) -> True/False
def __get__(self, instance, owner):
# if an 'instance' is passed
# return dict of {ability attr: [ability value]}
# else use 'owner'
# return dict of {ability attr: ability obj}
_d = {}
if instance is None:
if self._get_break(owner):
return None
self._set_break(owner)
attrs = [a for a in dir(owner) if a not in std_class_methods]
for attr in attrs:
obj = getattr(owner, attr)
if getattr(obj, '_is_ability_method', False):
_d[attr] = obj
self._release_break(owner)
return _d
else:
if self._get_break(instance):
return None
self._set_break(instance)
ability_accessor = _AbilityAccessor()
attrs = [a for a in dir(instance) if a not in std_instance_methods]
for attr in attrs:
obj = getattr(instance, attr)
# check if the obj is an ability method
if getattr(obj, '_is_ability_method', False):
ability_accessor += _Ability(attr, obj)
# else check if the obj is a class with abilities
elif getattr(obj, '_utilizes_abilities', False):
# get that obj's abilities and extend ours
ability_accessor += obj.abilities
self._release_break(instance)
return ability_accessor
def __set__(self, instance, value):
raise ValueError("Cannot change an '_AbilityLookup'")
def __delete__(self, instance, value):
raise ValueError("Cannot delete an '_AbilityLookup'")
def _get_break(self, obj):
return self._breaks.get(id(obj), False)
def _set_break(self, obj):
self._breaks[id(obj)] = True
def _release_break(self, obj):
self._breaks[id(obj)] = False
def abilitymethod(func):
""" method decorator to mark it as an 'abilitymethod' """
# check if func has an 'invalid' name
if func.func_name in dir(_AbilityAccessor):
raise ValueError("Invalid name for an abilitymethod! '%s'" %\
(func.func_name,))
func._is_ability_method = True
return func
class ClassWithAbilities(object):
""" inherit from this to provide ability introspection """
_utilizes_abilities = True
abilities = _AbilityLookup()
# ------------- /Abilities -------------------------------
if __name__ == "__main__":
class RobotFirmware(ClassWithAbilities):
@abilitymethod
def power_on(self):
print 'RobotFirmware.power_on'
self.power_on_checks()
def power_on_checks(self):
""" demonstrates object encapsulation of methods """
print 'RobotFirmware.power_on_checks'
class UpgradedRobotFirmware(RobotFirmware):
@abilitymethod
def laser_eyes(self, wattage):
print "UpgradedRobotFirmware.laser_eyes(%d)" % wattage
class RobotArm(ClassWithAbilities):
@abilitymethod
def power_on(self):
print 'RobotArm.power_on'
@abilitymethod
def bend_girder(self):
print 'RobotArm.bend_girder'
class Robot(ClassWithComponents, ClassWithAbilities):
firmware = Component(RobotFirmware)
arm = Component()
@abilitymethod
def power_on(self):
print 'Robot.power_on'
def kill_all_humans(self):
""" demonstrates a method that components didn't take over """
print 'Robot.kill_all_humans'
print '-- Components --------'
print 'Robot.components:', Robot.components
r = Robot()
print 'r.components: ', r.components
print '\tuploading firmware to robot...'
try:
r.firmware = RobotArm()
except Exception, e:
print "\tMALFUNCTION! %s" % (e,)
print '\tuploading firmware to robot try #2...'
r.firmware = RobotFirmware()
print '\t...success'
print 'r.components: ', r.components
del(r)
print '----------------------'
print ''
print '-- Abilities ---------'
print "Robot.abilities:", Robot.abilities
r = Robot()
print "r.abilities: ", r.abilities
print "r.abilities (by name): ", [ab.name for ab in r.abilities]
print '\tuploading firmware to robot...'
r.firmware = RobotFirmware()
print "r.abilities (by name): ", [ab.name for ab in r.abilities]
print "r.firmware.abilities: ", r.firmware.abilities
print '\tattaching arm to robot...'
r.arm = RobotArm()
print "r.abilities (by name): ", [ab.name for ab in r.abilities]
print "\twhat abilities does 'UpgradedRobotFirmware' provide?"
print "\t", [x for x in UpgradedRobotFirmware.abilities]
print "\tOooh laser eyes! upgrading...",
r.firmware = UpgradedRobotFirmware()
print "...done"
print "\tPowering on..."
r.abilities.power_on()
print "\tTesting out laser eyes"
r.abilities.laser_eyes(300)
print "\tDeleting firmware"
r.firmware = None
print "\tPowering on..."
r.abilities.power_on()
print '----------------------'
|
Alright, as I said in my description this is a re-implementation of Recipe 576852, and I believe that there is enough difference to provide another recipe. If there is a better 'standard' way to link two recipes please let me know. The ways in which I believe that this way is superior than the other recipe are listed:
- The class (Robot) in my example must specify through inheritance that it is a class that has abilities and components and they will not be attached/utilized without its awareness
- An instance's 'abilities' are now localized and called through the 'abilities' attribute instead of methods being assigned on the instance and appearing like regular methods
- (goes with 2) An instances abilities are grouped together to provide more flexibility for introspection by outside objects that want to query what abilities the instance provides.
- If you don't want the ability call to go through the tree, the instance can bypass the 'combined' abilities by calling the method locally instead of through the 'abilities' attribute. (e.g. r.power_on() instead of r.abilities.power_on())
A bit more discussion on the component stuff. It really is nothing too special and the 'abilities' mechanisms would work fine without the 'component' mechanisms (and vice versa). However, I believe that they work well together which is why I included both in my code.
This recipe probably won't set any speed/efficiency records because the instance's abilities are regenerated upon every call to attributes.__get__ among other reasons, but I believe that this provides for much more dynamic introspection. I can provide a generalized description of how this works, and would be glad to answer any questions. Play with it, tell me where it's lacking and pick it apart. Thanks!
So after lengthy reading concerning a design somewhat similar to this, I see that "component architecture" is probably not the correct/proper software design describing this structure. It is probably a mix of strategy pattern, multi-dispatch, and a couple others.