#19585: Improve efficiency of calling GAP functions
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Reporter: jaanos | Owner:
Type: enhancement | Status: needs_work
Priority: major | Milestone: sage-6.10
Component: interfaces | Resolution:
Keywords: GAP functions | Merged in:
interface | Reviewers: Travis Scrimshaw
Authors: Janoš Vidali | Work issues:
Report Upstream: N/A | Commit:
Branch: | 31a173bccd732cb8d8b656d6882dcec074a87b7d
u/jaanos/improve_calling_gap_function-19585| Stopgaps:
Dependencies: |
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Changes (by jaanos):
* status: needs_review => needs_work
Comment:
Hello everybody!
It turns out that we still have some issues here.
Firstly, GAP function calls don't actually work when done through a
temporary file, nor does getting a variable (which is essentially a
`Print` call). The reason for this is that when `_eval_line_using_file` is
called, it first looks for a `:=` token - if there is one, all is well;
but since we are relying on `last`, we don't have one, and a `Print()` is
wrapped around our function call. If the function actually returns a
value, this gives an impression of working, since the correct result is
printed - but we get an `AsciiArtString` instead of a `GapElement`. When
the function does not return a value, the situation is even worse, since
printing the result of a function which does not return a result results
in an error (which is silently suppressed, and an empty string is
returned).
Now, it seems that we can't really solve this problem, since `last` is not
updated when commands are read from a file. So I'd suggest this is how we
deal with it:
* If the command is short, evaluate it directly (one or two `eval`s, as in
the latest commit).
* If the command is long, we assign its result to a variable. This will of
course cause an error if the function does not return a value - but such
functions are few and it is much more likely that a (long) function does
return a value.
* When getting a variable, we make a direct call to
`Expect._eval_line_using_file` if a file should be needed to avoid having
two `Print`s and hence an error.
This problem has existed before this ticket was opened, so the cases when
a temporary file is used are marginal at best. If you think it is OK, I
can implement the above solution (or maybe someone else can do it, since
I'll probably be busy in the following days).
Secondly, `get_using_file` is indeed meant to use a file to read the
results. So the code regarding `_get_using_file` should probably be left
as it is (of course we can always set `_get_using_file`, so we don't need
`try`/`except` blocks to check it), although the length of the input may
be a poor predictor of the length of the output. Now, we should check
whether getting with a file is actually faster with GAP than directly
reading the output.
Janoš
--
Ticket URL: <http://trac.sagemath.org/ticket/19585#comment:28>
Sage <http://www.sagemath.org>
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