On Jun 25, 2:30 pm, Carl Banks <pavlovevide...@gmail.com> wrote:
Thank you for the very good reply. In fact delegating is the approach
that works. The main thing to notice is that for an uninstantiated
class the first arg to __get__ is None:
class desc(object):
__slots__ = ('x')
def __init__(self, desc):
self.x = desc
def __get__(self, a, b):
#print 'desc get', `self`, `a`, `b`
if a == None:
return self
return self.x.__get__(a)
def __set__(self, a, b):
#print 'desc set', `self`, `a`, `b`
self.x.__set__(a, b)
def foo(self):
return 'foo'
def bar(self):
return 'bar'
class A(object):
__slots__ = ('x', 'y')
def __init__(self, *args):
for i in xrange(len(args)):
setattr(self, A.__slots__[i], args[i])
a = A(0, 1)
b = A(2, 3)
print a.x, a.y, b.x, b.y
x = A.x
dx = desc(x)
A.x = dx
y = A.y
dy = desc(y)
A.y = dy
print type(a).x.foo()
print type(a).x.bar()
print type(a).y.foo()
print type(a).y.bar()
print type(b).x.foo()
print type(b).x.bar()
print type(b).y.foo()
print type(b).y.bar()
print a.x, a.y, b.x, b.y
a.x = -1
a.y = -2
b.x = -3
b.y = -4
print a.x, a.y, b.x, b.y
A.x = x
print a.x, a.y, b.x, b.y
This produces this output:
0 1 2 3
foo
bar
foo
bar
foo
bar
foo
bar
0 1 2 3
-1 -2 -3 -4
-1 -2 -3 -4
The manner in which __get__ has to delegate is not pleasant compared
to if you could simply derive a new class from method_descriptor with
the foo and bar methods though, oh well.
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