On Tuesday 25 January 2005 12:40, Richie Hindle wrote:
>
> [Steven]
> > Can someone give me an example of where __-mangling really solved a
problem
> > for them, where a simple leading underscore wouldn't have solved the
> > same problem?
>
>
http://cvs.sourceforge.net/viewcvs.py/spambayes/spambayes/spambayes/Dibbler.py?r1=1.13&r2=1.13.4.1
>
> That's a bugfix to SpamBayes, where I'd inadvertently named an instance
> variable '_map' without realising that the base class
> (asynchat.async_chat) also had an instance variable of that name. Using
> double underscores fixed it, and had I used them from the beginning the
> bug would never have cropped up (even if asynchat.async_chat had an
> instance variable named '__map', which is the whole point (which you know,
> Steven, but others might not)).
I have a counterexample. Consider refactoring a class from....
class B(A):
etc
....into....
class C(A):
etc
class B(C):
etc
Usage of some double-undescore attributes moved from B to the new intermediate
base class C. Unit tests on B still passed, so that change is safe. right?
The problem occured because the double-underscore mangling uses the class
name, but ignores module names. A related project already had a class named C
derived from B (same name - different module). My refactoring caused
aliasing of some originally distinct double-underscore attributes.
--
Toby Dickenson
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