#12601: @cached_method does not work for special methods
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Reporter: saraedum | Owner: jason
Type: enhancement | Status: new
Priority: minor | Milestone: sage-5.12
Component: misc | Resolution:
Keywords: cached_method, cache, | Merged in:
operator, special method | Reviewers:
Authors: | Work issues:
Report Upstream: Reported upstream. No | Commit:
feedback yet. | Stopgaps:
Branch: |
Dependencies: |
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Comment (by SimonKing):
I think I found the problem. Since the special method of the class is
called, the `__get__` method of `CachedMethod` is relevant. Its purpose is
to return a "cached method caller" that is bound to the instance.
This `__get__` method currently supposes that it is ''only'' called if the
attribute is not overridden on the instance's `__dict__`. Namely, if the
`CachedMethodCaller` is in the instance's `__dict__`, then Python's
attribute lookup will not care about the `CachedMethod` if the instance's
class.
Hence, `__get__` currently does
{{{
#!python
# This is for Parents or Elements that do not allow attribute
assignment:
try:
name = self._cachedfunc.__name__
except AttributeError:
name = self.__name__
try:
return (<dict>inst.__cached_methods).__getitem__(name)
except (AttributeError,TypeError,KeyError),msg:
pass
}}}
and would then create a ''new'' `CachedMethodCaller`. However, in the
example from the ticket description, there already is a
`CachedMethodCaller` in the instance's `__dict__`, but it is ignored by
the `__get__` method of the `CachedMethod`.
So, a potential solution is to additionally check
`inst.__dict__.__getitem__(name)`.
What I don't like about this solution is that it would involve an
additional dictionary lookup, which would slow-down every call to a cached
method, fortunately only in the case that the instance does not support
attribute assignment. And in addition, the call to the special method will
''always'' involve running this `__get__` method and doing a dictionary
lookup.
Alternatively, one could create a special kind of cached method,
specifically for special methods of new style classes whose instances
allow for attribute assignment.
--
Ticket URL: <http://trac.sagemath.org/ticket/12601#comment:8>
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