#11298: Extend the capabilities of Sage's introspection
-------------------------+--------------------------------------------------
Reporter: SimonKing | Owner: jason
Type: defect | Status: needs_review
Priority: major | Milestone: sage-4.7.1
Component: misc | Keywords: edit sageinspect
Work_issues: | Upstream: N/A
Reviewer: | Author: Simon King
Merged: | Dependencies: #9976
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Comment(by SimonKing):
Replying to [comment:20 jhpalmieri]:
> This looks pretty good to me. I have one question: in
`sage_getsourcelines`, lines 1408-1411, you have the code
> ...
>
> What is `type` here? Can you give me an example which will reach this
code?
By `type`, I mean the type `type`, such as here:
{{{
sage: 1.__class__
<type 'sage.rings.integer.Integer'>
sage: 1.__class__.__class__
<type 'type'>
}}}
The idea of the code lines in question is as follows:
Let `obj` be the object whose source lines we want to determine. It is not
necessarily true that the correct source lines for `obj` coincide with the
source lines of its class (notorious counter example: decorated methods).
Therefore, we need to try harder.
- First, it is attempted to get the position of the source code from what
`inspect.getdoc` returns (lines 1400-1401)
- Second (if "first" fails), the same is attempted with what
`_sage_getdoc_unformatted` returns (lines 1403-1404). For a reason that I
don't understand, one can not replace the first step by the second step:
The comment that I inserted states that a mysterious import error would
occur at startup.
- Third (if "second" fails as well), it is tested whether the inspect
module can provide the source lines of the object `obj` (line 1407).
- Last resort (if "third" fails), we replace `obj` by `obj.__class__`.
That is not desired for decorated methods, but these are supposed to
provide the source lines in a different way, so that one of the first
three methods should succeed. I think as a last resort it is ok... (line
1410).
There is one obvious problem with the "last resort". If the source lines
of `obj.__class__` can not be found (e.g., if `obj.__class__` is defined
in an spkg, not in the Sage library) then as a last resort one would try
to get `obj.__class__.__class__`, but that is the type `type` (see
example above), which is defined in the Python spkg and can thus not be
found. Infinite recursion.
In order to avoid the infinite recursion, an error is raised if
`obj.__class__` is the type `type`, which is, in particular, the case if
`obj` is not a class instance but a class.
I hope that answers your question...
--
Ticket URL: <http://trac.sagemath.org/sage_trac/ticket/11298#comment:22>
Sage <http://www.sagemath.org>
Sage: Creating a Viable Open Source Alternative to Magma, Maple, Mathematica,
and MATLAB
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