#12353: wrong comparison between RealIntervalField and RealField
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Reporter: zimmerma | Owner: AlexGhitza
Type: defect | Status: new
Priority: blocker | Milestone: sage-5.0
Component: basic arithmetic | Keywords:
Work_issues: | Upstream: N/A
Reviewer: | Author:
Merged: | Dependencies:
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Comment(by fbissey):
Are we talking about this piece of code (line 840)
{{{
except (TypeError, NotImplementedError):
r = cmp(type(left), type(right))
if r == 0:
r = -1
}}}
As far as I know comparing type when you cannot compare the values is
standard python behavior and is implemented in other places such as
sets/set.py
{{{
def __cmp__(self, right):
r"""
Compare self and right.
If right is not a Set compare types. If right is also a Set,
returns comparison on the underlying objects.
.. note::
If `X < Y` is true this does *not* necessarily mean
that `X` is a subset of `Y`. Also, any two sets can be
compared still, but the result need not be meaningful
if they are not equal.
EXAMPLES:
sage: Set(ZZ) == Set(QQ)
False
sage: Set(ZZ) < Set(QQ)
True
sage: Primes() == Set(QQ)
False
The following is random, illustrating that comparison of
sets is not the subset relation, when they are not equal::
sage: Primes() < Set(QQ) # random
True or False
"""
if not isinstance(right, Set_object):
return cmp(type(self), type(right))
return cmp(self.__object, right.__object)
}}}
The comparison of type can be machine dependent as far as I remember which
explain the inconsistencies. I guess it would be nice to try to get
* a better answer
* a better comparison
--
Ticket URL: <http://trac.sagemath.org/sage_trac/ticket/12353#comment:5>
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