#14187: Check that lazy imports are not resolved during startup
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Reporter: vbraun | Owner: tbd
Type: enhancement | Status: needs_review
Priority: major | Milestone: sage-5.8
Component: performance | Resolution:
Keywords: | Work issues:
Report Upstream: N/A | Reviewers: Nicolas M. Thiéry
Authors: Volker Braun | Merged in:
Dependencies: | Stopgaps:
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Comment (by robertwb):
Replying to [comment:28 nbruin]:
> See [http://bugs.python.org/issue793822 this python bug]. The following
code segfaults:
> {{{
> from gc import get_referrers
>
> def iter():
> tag = object()
> yield tag # 'tag' gets stored in the result tuple
> lst = [x for x in get_referrers(tag)
> if isinstance(x, tuple)]
> t = lst[0] # this *is* the result tuple
> print t[3] # full of nulls !
>
> tuple(iter())
> }}}
> Before we use `get_referrers` in production code you'd need to
understand what goes wrong in the above example and guarantee this won't
happen for the dictionaries we do replacements on.
This is intentionally creating a partially-constructed tuple and using the
fact that get_referrers() can refer to it. "partially-constructed" dicts
are safe, if we ever run across one.
> I'd think that looming segfaults are a high price to pay for the
convenience of writing `NN=module.NN` rather than
`lazy_import("other_module",NN)`.
The convenience is in being abel to write "from sage.foo.all import X" and
not worry about whether X was (possibly transitively) lazily imported. I
think that's a big win.
--
Ticket URL: <http://trac.sagemath.org/sage_trac/ticket/14187#comment:30>
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