Le jeudi 07 septembre 2006 15:33, Steven Bethard a écrit :
Well, lambda's not going away[1],
Sure, they won't.
but there's no *need* for lambda here.
It could be written as::
Le jeudi 07 septembre 2006 17:16, George Sakkis a écrit :
Sure, it *could*; whether it *should* is a different issue. I can't
imagine a case for absolute *need* of lambda, but there are several
cases where it is probably the best way, such as the one of this
thread.
I have no preferences here, I used lambdas because it's more compact but they
have also their drawback, when the function get a little more complex the
code is quickly confusing. The main advantage of the lambdas in this case is
to not pollute the class namespace.
Le jeudi 07 septembre 2006 23:48, Steven Bethard a écrit :
The code i wrote was to demonstrate late binding is usually not needed (and
it's not the semantic of properties so it's a bit like "make Java in
Python").
Only the second recipe has to do with it, but is not clean IMHO, it's
unnecessary complicated and it introduce a extra level of indentation which
is rather confusing, the 'self' variable in accessors is not what it seems to
be. Moreover, it introduce a new semantic for a functionality which is
already part of the language, what's the goal ? To lost python developers
reading your code ?
If you really want late binding, the first recipe may be a solution, but it
should be both simpler and should not introduce a new semantic (the functions
passed as strings is disappointing).
I'd write it like this :
class LateBindingProperty(property) :
__doc__ = property.__dict__['__doc__'] # see bug #576990
def __init__(self, fget=None, fset=None, fdel=None, doc=None) :
if fget : fget = lambda s, n=fget.__name__ : getattr(s, n)()
if fset : fset = lambda s, v, n=fset.__name__ : getattr(s, n)(v)
if fdel : fdel = lambda s, n=fdel.__name__ : getattr(s, n)()
property.__init__(self, fget, fset, fdel, doc)
In [4]: class A(object) :
...: def getx(self) : return self._x
...: def setx(self, v) : self._x = v
...: p=LateBindingProperty(getx, setx)
...:
...:
In [5]: class B(A) :
...: def setx(self, v) : A.setx(self, 2*v)
...:
...:
In [8]: a=A()
In [9]: a.p = 5
In [10]: a.p
Out[10]: 5
In [11]: a._x
Out[11]: 5
In [12]: b=B()
In [13]: b.p=5
In [14]: b.p
Out[14]: 10
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