#9989: easier access to operands of a symbolic expression
----------------------------------------------------+-----------------------
Reporter: burcin | Owner: burcin
Type: enhancement | Status:
needs_review
Priority: major | Milestone:
sage-4.7.1
Component: symbolics | Keywords:
Work_issues: | Upstream: N/A
Reviewer: Robert Bradshaw, Karl-Dieter Crisman | Author: Burcin
Erocal
Merged: | Dependencies:
----------------------------------------------------+-----------------------
Changes (by burcin):
* status: needs_work => needs_review
* reviewer: Robert Bradshaw, Karl-DIeter Crisman => Robert Bradshaw,
Karl-Dieter Crisman
Comment:
Thank you for the thorough reviews. I appreciate the feedback and it's
certainly good for someone to look over my changes, since there are often
rough edges I fail to see after staring at the code for a while.
Replying to [comment:11 kcrisman]:
> Questions, though.
> * Regarding the error message:
> {{{
> sage: f = 3*x^2+2*sin(x)-32*sin(ln(x))
> sage: f.op[3]
>
---------------------------------------------------------------------------
> IndexError Traceback (most recent call
last)
> IndexError: operand index out of range, got 3, expect between -3 and 3
> }}}
> Is this really the error message we want? Here it's the 'exclusive'
between, but that could be confusing. Maybe it should say between -3 and
2 (length ops -1)?
Fixed.
> * Next, I wonder whether the following can be supported:
> {{{
> sage: f.op[2:3,3]
> TypeError: an integer is required
> }}}
> since matrices can do this
> {{{
> sage: M = matrix(4,range(16))
> sage: M[2:3]
> [ 8 9 10 11]
> sage: M[2:3,3]
> [11]
> }}}
> The current code ends everything if it's a slice; you just get the
operands at that level. But it would be interesting to get the 2nd
element of each operand, though perhaps not very useful since you might
not know what it is ahead of time. But perhaps for very regular
expressions (Christoffel symbol-type surfeit of indices?) it could be
useful. We might also want something like `sage: M[2:3,3:4]` to be
supported, such as `sage: f.op[2,0:1]` instead of having to do
> {{{
> sage: f.op[2].op[0:1]
> [sin(log(x))]
> }}}
> But maybe going back and forth between Ginac and Sage in the way
you'd have to for that is tricky.
The output is a list if the index is a slice. We could pass further
indices to the list's `__getitem__()` of course, though I'm not convinced
this convenience is really a good feature.
> * Here is something needed for sure:
> {{{
> sage: f = 3*x^2+2*sin(x)-32*sin(ln(x))
> sage: f[1]
>
---------------------------------------------------------------------------
> TypeError Traceback (most recent call
last)
> TypeError: 'sage.symbolic.expression.Expression' object does not support
indexing
> sage: search_src('does not support indexing')
> <no response>
> }}}
> We should have at least one doctest ''somewhere'' that tests this.
I added a test in the docstring for `__get__` in `expression.pyx`.
For patchbot:
Apply trac_9989-operands.take3.patch
--
Ticket URL: <http://trac.sagemath.org/sage_trac/ticket/9989#comment:12>
Sage <http://www.sagemath.org>
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