There are two ways that sage sends data to GAP. The first is to send it line
by line, and the second is to send it via a file. This last is used when there
is a lot of data because, IIRC, it's faster. However, this messes up the use
of stdout e.g. Print. So what's happening is if the input is long enough, it
goes to a file. That's why removing some of the prints makes a difference.
You can also get the same effect by adding a bunch of spaces in the middle
(they are stripped from the beginning and the end).
One way around this is to use
gap.eval(...., allow_use_file=False)
which allows you to see that this is in fact the cause of the problem. The
second method is to change the cutoff (default is 100)
gap._eval_using_file_cutoff = 1000
or disable it entirely
self._eval_using_file_cutoff = None
You can set it in ~/.sage/init.sage to make it "permanent".
As for a truly permanent solution, we could try disabling it if we see a
function that prints to stdout like Print or Display, but it wouldn't work for
custom functions. I don't think there is a way around this based on how GAP is
currently written (except not using a file), but I could be wrong.
-Ivan
On Jun 29, 2012, at 5:05 AM, kcrisman wrote:
> On Thursday, June 28, 2012 10:39:01 PM UTC-4, kcrisman wrote:
> Hi Walter!
>
> On Thursday, June 28, 2012 8:11:55 PM UTC-4, Walter Carlip wrote:
> I am having trouble using Gap within Sage. Often things fail to print or to
> work from Sage even though they do work directly in Gap. How do I report
> bugs and get help? Here is a sample program my tutors devised that does not
> print under Sage, but works fine directly in Gap:
> for n in [1..10] do
> for m in [1..10] do
> Print(m*n);
> Print(" - ");
> od;
> Print("\n");
> od;
>
> (Removing the second Print command makes it work. We have found many other
> things like this that seem to fail without explanation.
>
>
> Are you using this in the notebook? I can confirm this behavior in a %gap
> cell.
>
> There was, once upon a time, a problem with comments - see
> http://trac.sagemath.org/sage_trac/ticket/3752 . I feel like I've seen this
> before as well in the lists, but can't quite find it yet. #5043 and #3152
> are conceivably, but unlikely to be, related. I'll keep looking.
>
>
>
> We can see exactly what is going on with this in the source code at
> http://hg.sagemath.org/sage-main/file/9ab4ab6e12d0/sage/interfaces/gap.py#l365
>
> Notice that this has nothing to do with the notebook - if you make a raw
> Python string
>
> str = r"""
> for n in [1..10] do
> for m in [1..10] do
> Print(m*n);
> Print(" - ");
> od;
> Print("\n");
> od;
> """
>
> and do gap.eval(str) in Sage, the same problem happens.
>
> Maybe one of the tutors can track down. Notice that
>
> str1 = r"""
>
> for n in [1..10] do
> for m in [1..10] do
> Print(m*n);
> Print(" - ");
> od;
> od;
> """
> gap.eval(str1)
>
> erroneously adds newlines.
>
> '1 - 2 - 3 - 4 - 5 - 6 - 7 - 8 - 9 - 10 - 2 - 4 - 6 - 8 - 10 - 12 - 14 -
> 16 - \n18 - 20 - 3 - 6 - 9 - 12 - 15 - 18 - 21 - 24 - 27 - 30 - 4 - 8 -
> 12 - 16 - \n20 - 24 - 28 - 32 - 36 - 40 - 5 - 10 - 15 - 20 - 25 - 30 -
> 35 - 40 - 45 - \n50 - 6 - 12 - 18 - 24 - 30 - 36 - 42 - 48 - 54 - 60 - 7
> - 14 - 21 - 28 - 35 - \n42 - 49 - 56 - 63 - 70 - 8 - 16 - 24 - 32 - 40 -
> 48 - 56 - 64 - 72 - 80 - 9 - \n18 - 27 - 36 - 45 - 54 - 63 - 72 - 81 -
> 90 - 10 - 20 - 30 - 40 - 50 - 60 - \n70 - 80 - 90 - 100 -'
>
> Oh, that's the problem.
>
> gap.eval(str,newlines=False)
>
> gives the correct answer. Now the question is, why?
>
> This is now http://trac.sagemath.org/sage_trac/ticket/13178. Gap experts are
> welcome here; maybe a newline is surreptitiously entered at the end of a "od"?
>
> - kcrisman
>
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