Dag Sverre Seljebotn, 03.12.2009 12:45:
> Stefan Behnel wrote:
>> Dag Sverre Seljebotn, 03.12.2009 10:52:
>>
>>>> - Python's floating point type is double, so it should be perfectly
>>>> safe to do
>>>>
>>>> cdef double f(): ...
>>>> x = f() # infer x as double
>>>>
>>>> By the same argument one might actually want to do
>>>>
>>>> cdef float f(): ...
>>>> x = f() # infer x as *double* -- because that's what Python would use
>>>>
>> That's actually an orthogonal feature: aliasing Python's float type to C's
>> double type in general, including support for methods etc. Since 'double'
>> is immutable and has exactly the same value range as Python's float type,
>> this is something that can always be done safely. If I'm not mistaken, even
>> Python's operators behave exactly like the equivalent C operators here,
>> right? And numeric operations would always return a double, so even
>> operations on doubles that involve integers would run completely in C space.
>>
>> Apart from a couple of further optimisations for methods and properties, I
>> think enabling type inference here would give us a rather warmly requested
>> feature.
>>
> This is now http://trac.cython.org/cython_trac/ticket/460.
Rethinking this some more, there are a couple of problems with this, e.g.
overflow errors:
>>> 2.0**1000000
Traceback (most recent call last):
OverflowError: (34, 'Numerical result out of range')
Moving this calculation to C space means we have to catch the error and
raise an exception for it.
Then, while simplistic code like this will work beautifully:
d = 1.0
for i in range(1000):
d += 1.0
print d
most code won't currently benefit from enabling type inference for doubles,
as it's rather unlikely that all operations done on a variable only use
other (implicitly/explicitly) typed names as operands. And as long as there
is one assignment with unknown types on the rhs, the name will be typed as
Python object (which is required since the value could be anything, e.g.
some kind of vector object). So we clearly have to do more here to make
this useful.
Stefan
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