#7857: Arithmetic operations in fraction fields
---------------------------+------------------------------------------------
Reporter: spancratz | Owner: spancratz
Type: enhancement | Status: needs_review
Priority: major | Milestone: sage-4.3.1
Component: algebra | Keywords: fraction field
Work_issues: | Author: spancratz
Upstream: N/A | Reviewer: John Cremona
Merged: |
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Changes (by spancratz):
* status: needs_work => needs_review
Comment:
Firstly, I wanted to say that the most recent patch file now passes all
doctests on my machine.
It is definitely true that a lot of errors are silenced. But this is done
in essentially the same way as before, where, whenever ``reduce`` was
called from ``__init__``, the three kinds of errors (``AttributeError``,
``NotImplementedError``, and ``TypeError``) were converted to an
``ArithmeticError``, which was then silenced in ``__init__``. That is,
the user would only actually see the errors if he called ``reduce``
directly.
Of course, I am not entirely sure about this, but I think the behaviour
might have been intended. For example, I don't think someone using
fraction fields of non-Euclidean PIDs or Euclidean domains without a GCD
implementation should have to wrap all his basic arithmetic calls in ``try
... except``. On the other hand, if someone explicitly calls ``reduce``,
the exceptions should be raised and the caller ought to deal with them.
What do you think, Robert?
About the second point, I had the impression that for rings the method
``inverse_of_unit`` was either implemented or not, rather than it being
implemented only to return a ``NotImplementedError``, which is why I am
only catching ``AttributeError``s. However, if this is not the case, then
I agree with you, ``NotImplementedError``s should be handled in exactly
the same way as ``AttributeError``s in this place. Could you please
comment on this?
Thanks,
Sebastian
Replying to [comment:10 robertwb]:
> You seem to be catching and silencing a huge number of errors, without
explanation (though the code before wasn't too good at that either). Also,
what if inverse_of_unit raises a NotImplementedError, shouldn't it still
be as reduced as possible?
--
Ticket URL: <http://trac.sagemath.org/sage_trac/ticket/7857#comment:11>
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