#11316: Weighted degree term orders added
--------------------------------+-------------------------------------------
Reporter: klee | Owner: AlexGhitza
Type: enhancement | Status: needs_review
Priority: minor | Milestone: sage-4.7.1
Component: basic arithmetic | Keywords:
Work_issues: | Upstream: N/A
Reviewer: | Author: Kwankyu Lee
Merged: | Dependencies:
--------------------------------+-------------------------------------------
Comment(by SimonKing):
Replying to [comment:11 klee]:
> I kept double underscores in the new patch. I don't know why Martin do
not like double underscore attributes. Do you think single underscore
attributes are generally preferable over double ones? Or is it just for
fixing unpickling problem.
As Martin said, double underscore attributes can be a problem in sub-
classes. To be precise: We talk about an attribute whose name starts with
two underscores but ends with less than two underscores. It is a Python
convention that those attributes are private. And in order to emphasize
the privacy, Python applies so-called name mangling (easy to google): The
attribute name is mangled with the name of the class ''for which it was
originally defined''.
By consequence, there is a problem for subclasses:
{{{
sage: class A:
....: def __init__(self,n):
....: self.__n = n
....:
sage: class B(A):
....: def __init__(self,n):
....: A.__init__(self,n^2)
....:
sage: b = B(5)
sage: b.__n
---------------------------------------------------------------------------
AttributeError Traceback (most recent call
last)
/home/king/<ipython console> in <module>()
AttributeError: B instance has no attribute '__n'
}}}
So, surprise: `__n` seems gone. But it is there, under a different name:
{{{
sage: b._A__n
25
}}}
It is obvious that, under these circumstances, single underscore names are
easier to deal with.
Remark: No mangling occurs if the name ''ends'' with two underscores.
That's why all the magical methods `__repr__`, `__add__` etc. can be
easily inherited.
--
Ticket URL: <http://trac.sagemath.org/sage_trac/ticket/11316#comment:14>
Sage <http://www.sagemath.org>
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