i'm confused which part that doesn't make sense?
this is my 2nd attempt to py, the 1st was on april this year, it was
just a month, i'm afraid i haven't got the fundamentals right yet. so
i'm gonna lay out how i got to this conclusion, CMIIW
**explanation of feeling (0) on my 1st post**
to me, descriptor is a particular kind of delegation, it takes the job
of coding the delegation by having a contract with programmers that
the tree meta operations (get, set, del) on attr are delegated to the
obj that is bound to the attr
are we agree that descriptor is a kind of delegation?
the mechanism that makes descriptor works is in __getattribute__,
__setattr__, __delattr__ of 'object' & 'type'
now, if i want a single descriptor obj to be delegated to multiple
tasks, i can't do it since __get__ doesn't get info that can be used
to determine which task to do
i must have diff descriptor obj for each task
class Helper:
def __init__(self, name):
self.name = name
def __get__(self, ins, cls):
if self.name == 'task0': ...
elif self.name == 'task1': ...
else: ...
class a:
task0 = Helper('task0')
task1 = Helper('task1')
if __get__ receives the name, then i could do
class Helper:
def __get__(self, ins, cls, name):
...
class a:
task0 = task1 = Helper()
but after explaining this, i have more doubt on my own stmt in the 1st
post "not passing name strengthens the coupling between delegator &
delegate". now i think it's more likely the opposite, it weakens the
coupling at the expense of more objs. moreover, is it wrong to justify
that descriptor is a kind of delegation?
my ego speaks:
- i think, if the name is passed on, programmers can choose to use it
or not (i don't know if it brokes any py principle, i only know KISS)
- i realize that using name as the info that descriptors use to
determine which task to do, is going to strongly couple the descriptor
& the classes that use it, meaning that the descriptor & the user
classes must agree on attr names to be used. a simple solution to it
is by mapping attr names & names used in the descriptor
class Helper:
def __init__(self, name_map=None):
self.name_map = name_map
def __get__(self, ins, cls, name):
if self.name_map is None:
if name == 'task0': ...
...
else:
if self.name_map[name] == 'task0': ...
...
class a:
do_this = do_that = Helper({'do_this':'task0', 'do_that':'task1'})
finally, like all shared things, shared descriptor objs require more
effort for synchronization
--
http://mail.python.org/mailman/listinfo/python-list
