#10467 closed enhancement (fixed)
Improve lookup of private attributes
Reported by: | SimonKing | Owned by: | tbd |
---|---|---|---|
Priority: | major | Milestone: | sage-4.6.2 |
Component: | categories | Keywords: | private attribute lookup |
Cc: | Merged in: | sage-4.6.2.alpha1 | |
Authors: | Simon King | Reviewers: | Robert Bradshaw |
Report Upstream: | N/A | Work issues: | |
Branch: | Commit: | ||
Dependencies: | Stopgaps: |
Description (last modified by )
By a private attribute, I mean an attribute whose name starts with two underscores and does not end with an underscore. Such an attribute is used, e.g., in the default __repr__
method of Sage objects.
It should be reasonable to assume that private attributes belong to a particular instance, not to its class or its category; after all, they are subject to Python's name mangling.
In particular, if P
is a parent/element, then P.__foo
is either defined for the instance P
or will not be available from P.category().parent_class
resp. from P.category().element_class
.
It turns out that this assumption holds thorought Sage: When one lets the __getattr__
methods of Parent/Element? immediately raise an AttributeError
when a private attribute is requested, then all doc tests still pass.
That is what my patch mainly does. In addition, it removes several occurences of an idiom like
if hasattr(self,'foo'): return self.foo
and replaces it with
try: return self.foo except AttributeError: pass
which saves half of the computation time when the attribute actually exists.
The advantage is a considerable speedup. Here are two examples (the last is actually a serious computation):
Without the patch:
sage: P.<x> = QQ[] sage: timeit('a=repr(x)') 625 loops, best of 3: 74.7 Âµs per loop sage: R.<x,y> = InfinitePolynomialRing(QQ) sage: I = R.ideal([x[1]^2+y[2]*y[3], x[2]*y[1]*x[3]-y[1]*y[2]]) sage: %time I.groebner_basis() CPU times: user 23.09 s, sys: 0.02 s, total: 23.11 s Wall time: 23.67 s [y_2*y_1^3 + y_2*y_1^2, y_2^2*y_1 - y_2*y_1^2, y_3*y_1 - y_2*y_1, x_1*y_2*y_1^2 + x_1*y_2*y_1, x_1^2 + y_2*y_1, x_2*y_2*y_1 - x_1*y_2*y_1, x_2*x_1*y_3 - y_2*y_1, x_3*y_2*y_1 - x_1*y_2*y_1, x_3*x_1*y_2 - y_2*y_1, x_3*x_2*y_1 - y_2*y_1]
With the patch:
sage: P.<x> = QQ[] sage: timeit('a=repr(x)') 625 loops, best of 3: 40.5 Âµs per loop sage: R.<x,y> = InfinitePolynomialRing(QQ) sage: I = R.ideal([x[1]^2+y[2]*y[3], x[2]*y[1]*x[3]-y[1]*y[2]]) sage: %time I.groebner_basis() CPU times: user 14.43 s, sys: 0.03 s, total: 14.46 s Wall time: 14.53 s [y_2*y_1^3 + y_2*y_1^2, y_2^2*y_1 - y_2*y_1^2, y_3*y_1 - y_2*y_1, x_1*y_2*y_1^2 + x_1*y_2*y_1, x_1^2 + y_2*y_1, x_2*y_2*y_1 - x_1*y_2*y_1, x_2*x_1*y_3 - y_2*y_1, x_3*y_2*y_1 - x_1*y_2*y_1, x_3*x_1*y_2 - y_2*y_1, x_3*x_2*y_1 - y_2*y_1]
The patch also adds doctests in Parent.__getattr__
, Element.__getattr__
and several methods of SageObject
.
Attachments (4)
Change History (26)
comment:1 Changed 9 years ago by
- Description modified (diff)
- Status changed from new to needs_review
comment:2 Changed 9 years ago by
comment:3 Changed 9 years ago by
I found yet another way to speed things up!
Typically, in Python one requests an attribute and catches an AttributeError
(this is also done in Python's hasattr
, IIRC). That happens very often during computations. Hence, it is very important that raising the error happens quickly.
The __getattr__
methods of sage.structure.parent.Parent and sage.structure.element.Element call a Python method sage.structure.parent.raise_attribute_error, that first creates the error message and then raises the AttributeError
. Interpreted Python is too slow for that purpose!
Therefore I updated my patch (will post it in a few minutes). Trick: Instead of
def raise_attribute_error(self, name)
it is now
cdef inline raise_attribute_error(self,name)
The effect of this little trick, compared with the benchmarks above, is:
(1) Saves almost 20% compared with the old patch, and more than 50% compared with unpatched Sage:
sage: P.<x> = QQ[] sage: timeit('a=repr(x)') 625 loops, best of 3: 33.8 Âµs per loop
(2) Saves almost 10% compared with the old patch and almost 50% compared with unpatched Sage:
sage: R.<x,y> = InfinitePolynomialRing(QQ) sage: I = R.ideal([x[1]^2+y[2]*y[3], x[2]*y[1]*x[3]-y[1]*y[2]]) sage: %time I.groebner_basis() CPU times: user 13.30 s, sys: 0.02 s, total: 13.32 s Wall time: 13.38 s [y_2*y_1^3 + y_2*y_1^2, y_2^2*y_1 - y_2*y_1^2, y_3*y_1 - y_2*y_1, x_1*y_2*y_1^2 + x_1*y_2*y_1, x_1^2 + y_2*y_1, x_2*y_2*y_1 - x_1*y_2*y_1, x_2*x_1*y_3 - y_2*y_1, x_3*y_2*y_1 - x_1*y_2*y_1, x_3*x_1*y_2 - y_2*y_1, x_3*x_2*y_1 - y_2*y_1]
(3) No significant difference in the third benchmark:
sage: timeit('a=QQ.summation',number=50000) 50000 loops, best of 3: 526 ns per loop sage: timeit('a=QQ.summation',number=50000) 50000 loops, best of 3: 524 ns per loop sage: timeit('a=QQ.summation',number=50000) 50000 loops, best of 3: 527 ns per loop
comment:4 Changed 9 years ago by
The (updated) patch avoids looking up private attributes in the category, avoids some needless "hasattr" calls, and gains additional speed by cythenising "raise_attribute_error".
comment:5 Changed 9 years ago by
- Status changed from needs_review to needs_work
- Work issues set to Test for raise_attribute_error
I need to further update the patch: Of course, after cythonising raise_attribute_error
, the doctest of that function fails, because one needs a Python function calling it.
comment:6 Changed 9 years ago by
- Status changed from needs_work to needs_review
- Work issues Test for raise_attribute_error deleted
The patch is updated, the doctests should now pass.
comment:7 follow-up: ↓ 9 Changed 9 years ago by
- Status changed from needs_review to needs_work
Mostly looks good. My only request is that in the repr and interface_init functions that an attribute error not be caught over the call into the sub-function, as that is not the intended behavior (and, speaking from first-hand experience, leads to un-intuitive to debug errors, particularly in methods like repr).
Changed 9 years ago by
comment:8 Changed 9 years ago by
- Status changed from needs_work to needs_review
Positive review to everything but my own (tiny) patch.
comment:9 in reply to: ↑ 7 Changed 9 years ago by
Replying to robertwb:
Mostly looks good. My only request is that in the repr and interface_init functions that an attribute error not be caught over the call into the sub-function, ...
You are right, that needs to be changed.
I applied your referee patch and (to be on the safe side) am running doctests. If it works then (if I understood correctly) I am entitled to change it into positive review, inserting your name as reviewer, right?
Best regards,
Simon
comment:10 Changed 9 years ago by
- Reviewers set to Robert Bradshaw
- Status changed from needs_review to positive_review
All tests pass with the referee patch. Hence, I change it to "positive review" and insert Robert as reviewer.
To the patchbot/release managaer:
Apply 10467attribute_lookup.patch 10467-attribute-referee.patch
Cheers,
Simon
comment:11 Changed 9 years ago by
Yes, that's all kosher. Thanks. BTW, the buildbot would pick up both patches just fine (though it only runs on needs-review tickets).
comment:12 Changed 9 years ago by
- Milestone changed from sage-4.6.1 to sage-4.6.2
comment:13 follow-up: ↓ 14 Changed 9 years ago by
Will the patch be merged, after meanwhile 5 weeks?
comment:14 in reply to: ↑ 13 Changed 9 years ago by
- Status changed from positive_review to needs_work
You should give the patch a proper commit message (use hg qrefresh -e
for that). Make sure the ticket number appears on the first line.
Changed 9 years ago by
comment:15 Changed 9 years ago by
- Status changed from needs_work to positive_review
Apply 10467attribute_lookup.patch 10467-attribute-referee.2.patch
Note: My patch had a proper commit message, and I hope that the referee does not mind that I added a commit message to the referee patch.
comment:16 Changed 9 years ago by
- Merged in set to sage-4.6.2.alpha1
- Resolution set to fixed
- Status changed from positive_review to closed
comment:17 Changed 4 years ago by
I'm undoing a large part of this patch of #20686. See that ticket for the rationale.
comment:18 Changed 4 years ago by
Hi, I am sitting next to Jeroen.
__getattr__
as implemented in this ticket makes it so that an error
is raised in the following situation:
sage: C = EuclideanDomains() sage: P.<x> = QQ[] sage: C.element_class.__foo = 'bar' sage: x.parent() in C True sage: x.__foo
However, when using plain Python inheritance, no error is raised in this equivalent situation:
sage: C = Semigroups() sage: S = C.example() sage: S.category() is C True sage: C.element_class.__foo = 'bar' sage: x = S.an_element() sage: x.__foo 'bar'
Given that the role of __getattr__
is to emulate Python inheritance
as closely as possible, I agree with Jeroen that the above behavior of
raising an error is not desirable. Especially since it has a cost.
Or would there be a use case for this behavior? I don't expect to see private methods in element_class'es; they probably would not work anyway.
Cheers,
Nicolas
comment:19 Changed 4 years ago by
Just checking that I can post a comment.
comment:20 Changed 4 years ago by
- Keywords just testing added
comment:21 Changed 4 years ago by
- Component changed from performance to categories
- Keywords just testing removed
comment:22 Changed 4 years ago by
I can post here, but not on #20686...
On sage-algebra, Nicolas Thiéry wrote:
Here are two data points.
(1) I compared "
sage -tp 4 sage/
" before and after applying the patch. It is 1810.3 seconds without the patch, but 1792.5 seconds with the patch. So, on average, it became quicker.(2) The timings improve if a non-existing private attribute is requested. So, let us test a situation where an existing categorical attribute is requested. For example, the method
summation
method of the rational field is only defined in its category.Without the patch, I obtained
With the patch, I obtain
So, that's a situation where it might expect a slight deceleration with the patch, but in fact it is as quick as before.