Dear Nils,
Thanks for the useful suggestions.
I probably used the wrong terminology, coercion vs conversion, sorry. What
I meant is simply that almost everywhere on Sage 8/2 is accepted as input
to a function that takes integer arguments, as it should IMHO. I
understand that preprocessing arguments in general may lead to trouble but
I think treating rational integers as integers is safe. Actually Sage does
that
sage: 8/2 in ZZ
True
So to have a function with integer input throw an error when you feed it a
rational integer, is surprising and counterintuitive. To me at least.
Best,
Nikos
On Sun, Jan 24, 2021 at 6:14 PM Nils Bruin <nbr...@sfu.ca> wrote:
> On Thursday, January 21, 2021 at 7:21:52 AM UTC-8 Nikos Apostolakis wrote:
>
>> Dear Vincent,
>>
>> Thank you very much, that fixes it.
>>
>> IMHO this is a bug though, or at least an inconsistent behavior. Most of
>> the time Sage silently coerces things to the appropriate type so commands
>> just work. For example:
>>
>
>
>>
>> sage: m = 11
>>> sage: l = (m-1)/2 -1
>>>
>> sage: l
>>> 4
>>> sage: range(5)[l]
>>> 4
>>
>>
>> There's a subtle difference here: The python interface here requires an
> index to be something that can be converted into an integer; i.e.,
> something for which the __int__ method does the right thing. "Coercion" in
> sage has a more restricted notion; see the docs. In sage, there is no
> coercion from QQ to ZZ, because there is no natural map from one to the
> other. There is a conversion, though, which is allowed to be a partial map.
>
> Generally, coercion maps only exist in one direction. Otherwise, things
> like ZZ(1)+QQ(2) whould have an ill-determined type.
>
> Whether "Words" should attempt to convert its second argument to an
> integer is a different matter. Generally it is best to start interface
> design by doing only a minimal amount of processing to the argument,
> because being "smart" for one thing can easily hide errors in another case.
>
> The error message that is currently given is perhaps a little generic, but
> it does clearly indicate that the arguments given to "Words" are
> problematic. Once you check that the *apparent* arguments work fine if
> entered directly, it's clear there's probably a type issue. If you use
> IPython's interactive debugger ("%debug") you can dive into the problematic
> code and query the arguments and their types directly, within the context
> where the error was raised. That can be a big time saver, because it can
> help you find the error without having to construct a stand-alone
> reproducible test case that you would need if you want to communicate the
> error to other people.
>
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