[sage-devel] Re: Status of @lazy_attribute for cdef classes

[Simon King]

Hi Jeroen,

On 2017-08-25, Jeroen Demeyer  wrote:
> On 2017-08-25 13:37, Simon King wrote:
>> Not much, actually:
>
> My point was that a __dict__ makes any attribute access slower, not just 
> this lazy attribute. It will also seriously slow down cpdef methods.

OK, if it concerns *all* cpdef methods then I understand that one should
be reluctant. @property supported by a cdef attribute works better anyway.

Cheers,
Simon

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Re: [sage-devel] Re: Status of @lazy_attribute for cdef classes

[Jeroen Demeyer]

On 2017-08-25 13:37, Simon King wrote:

Not much, actually:


My point was that a __dict__ makes any attribute access slower, not just 
this lazy attribute. It will also seriously slow down cpdef methods.


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[sage-devel] Re: Status of @lazy_attribute for cdef classes

[Simon King]

Hi Jeroen,

On 2017-08-25, Jeroen Demeyer  wrote:
> One workaround is adding a __dict__:
> ...
> This does make everything slower though, so I guess it's not what you want.

Not much, actually:
sage: cython("""
: from sage.structure.element cimport Element
: cdef class CyElement(Element):
: cdef object _test
: def __init__(self, P):
: Element.__init__(self,P)
: self.test = 15
: @property
: def test(self):
: return self._test
: @test.setter
: def test(self, x):
: self._test = x
: from sage.misc.lazy_attribute import lazy_attribute
: cdef class CyElement2(Element):
: cdef dict __dict__
: @lazy_attribute
: def test(self):
: return 15
: """)
sage: ec = CyElement(ZZ)
sage: ec2 = CyElement2(ZZ)
sage: %timeit ec.test
1000 loops, best of 3: 41 ns per loop
sage: %timeit ec2.test
1000 loops, best of 3: 45.4 ns per loop

That's even a little faster than attribute access in Python
(a lazy attribute on a Python class defined in a Cython file
takes 51.4 ns per loop).

Thank you for that trick!

Best regards,
Simon

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Re: [sage-devel] Re: Status of @lazy_attribute for cdef classes

[Jeroen Demeyer]

On 2017-08-25 13:07, Simon King wrote:

Hi!

I just realise that @property works for Cython, and it is
competitive!


Indeed. Cython has optimized code to deal with standard decorators like 
@staticmethod, @classmethod and @property.


The reason that lazy_import does not work for Cython classes is just 
that arbitrary attribute access is not allowed, i.e. obj.test = 15 
doesn't work, even if "test" is not a lazy attribute.


One workaround is adding a __dict__:

cdef class MyElement(Element):
cdef dict __dict__

@lazy_attribute
def test(self):
return 15

This does make everything slower though, so I guess it's not what you want.

I don't think there is a way to make @lazy_attribute work for types 
without a __dict__ (apart from specifically patching Cython to support 
@lazy_attribute).


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[sage-devel] Re: Status of @lazy_attribute for cdef classes

[Simon King]

Hi!

I just realise that @property works for Cython, and it is
competitive! Namely:

sage: cython("""
: from sage.structure.element cimport Element
: cdef class CyElement(Element):
: cdef object _test
: def __init__(self, P):
: Element.__init__(self,P)
: self.test = 15
: @property
: def test(self):
: return self._test
: @test.setter
: def test(self, x):
: self._test = x
: from sage.misc.lazy_attribute import lazy_attribute
: class PyElement(Element):
: @lazy_attribute
: def test(self):
: return 15
: """)
sage: ep = PyElement(ZZ)
sage: ep.test
15
sage: ec = CyElement(ZZ)
sage: ec.test
15
sage: %timeit ec.test
1000 loops, best of 3: 40.5 ns per loop
sage: %timeit ep.test
1000 loops, best of 3: 51.5 ns per loop

So, apparently a property getter in Cython is faster than an attribute
lookup in Python.

Cheers,
Simon

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