for loop with variable step not optimized

Spiro Python interface using Cython

Spiro is an algorithm for producing smooth splines given a set of
on-curve control points. I am working on polishing the library. I
wrote a Python interface using Cython (thanks to all those who develop
it!).

The Spiro library uses callbacks, hence my recent in doing that in
Cython. I am happy to say I have been successful. The attached code
demonstrates it to whoever can spend the time to read it. The code is
under the GPLv3+. (Note: you don't need to worry about the internals
of spiro.c -- just look at spiro.h and bezctx.h to understand the
library being wrapped.)

I have one question: Clang generates the warning:

spiro_cy.c:653:1: warning: declaration does not declare anything
[-Wmissing-declarations]
spiro_cp;
^~~~~~~~
1 warning generated.

Why is this and what should I do to fix it? Thanks.

-- 
Shriramana Sharma ஶ்ரீரமணஶர்மா श्रीरमणशर्मा

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OSX 10.8: setuptools generates gcc command that wants to use to use .c instead of .cpp

Sorting algorithm

cython's property and nondata descriptors

Two questions about cython's "property:" directive.

1] In python, a nondata descriptor is a descriptor that doesn't have
its '__set__' slot filled. Such descriptors can be overridden by
entries in the instance '__dict__'. One might expect that specifying a
cython "property" without giving a "__set__" method would lead to such
an entry, but it doesn't: It leads to a datadescriptor that cannot be
overridden by instance attributes:

%cython
cdef class T(object):
    property B:
        def __get__(self):
            return 1

>>> class S(T): pass
>>> s=S()
>>> s.B=10
AttributeError: attribute 'B' of 'T' objects is not writable

This mirrors the  <at> property decorator in python but it makes it hard to
specify nondata descriptors. Are there thoughts about how to make it
more convenient to declare nondata descriptors

2] Using the  <at> property decorator in a cdef class works, but leads to
less efficient code:

%cython
cdef class T(object):
    property B:
        def __get__(self):
            return 1
     <at> property
    def C(self):
        return 1

>>> t=T()
>>> timeit("t.B")
625 loops, best of 3: 78.6 ns per loop
>>> timeit("t.C")
625 loops, best of 3: 275 ns per loop

would it be desirable to automatically transcribe " <at> property" to
"property .."? Perhaps not, since the semantics of the two are
different and both are valid, but I expect it's a common pitfall for
people who try to translate python to cython code.

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static typing of mpf type variables in cython

build error using cython on OS X and Python 3.3 -- __time_t appearing from nowhere

Function pointer as part of a C struct

Hello everybody,

I want to use a callback as part of a C struct with read/write access. 
Is this possible? The following describes the problem. And if you can 
help, how do I connect a python function to the callback?

Any help welcome!

Regards
Alexander

---- stderr of compiling Device.pyx ---
Error compiling Cython file:
------------------------------------------------------------
...
     def __setattr__(self, name, value):
         print "DeviceDescriptor_.__setattr__", name, value
         if name == "deviceNumber":
             self._device_descriptor.deviceNumber = <Uint8> value
         elif name == "deviceMeasurement":
             self._device_descriptor.deviceMeasurement = 
<DeviceMeasureFunc> value
                                                        ^
------------------------------------------------------------
Device.pyx:55:56: Python objects cannot be cast to pointers of primitive 
types

----- Device.h ----
typedef ErrorStatus (*DeviceMeasureFunc)(Uint32*);

typedef struct DeviceDescriptorTag
{
	Uint8 deviceNumber;
	DeviceMeasureFunc deviceMeasurement;

} DeviceDescriptor;
------- Device.pyx ---
cdef extern from "Device.h":

     ctypedef ErrorStatus (*DeviceMeasureFunc)(Uint32*)

     ctypedef struct DeviceDescriptor_c "DeviceDescriptor":
         Uint8 deviceNumber
         DeviceMeasureFunc deviceMeasurement

cdef class DeviceDescriptor:

     cdef DeviceDescriptor_c _device_descriptor

     def __getattr__(self, name):
         ret_val = None
         if name == "deviceNumber":
             ret_val = self._device_descriptor.deviceNumber
         else:
             self.__raise_attrib_not_found(name)
         return ret_val

     def __setattr__(self, name, value):
         if name == "deviceNumber":
             self._device_descriptor.deviceNumber = <Uint8> value
         elif name == "deviceMeasurement":
             self._device_descriptor.deviceMeasurement = 
<DeviceMeasureFunc> value
         else:
             self.__raise_attrib_not_found(name)

     def __raise_attrib_not_found(self, name):
         raise AttributeError("Attribute %s not in %s" % (name, type(self)))

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TypeError: can't apply this __setattr__

For practice, I am implementing a subclass of builtins.list in Cython
which will store only str-s and has one data member "approved" which
should take only a boolean. It's entirely Python syntax except that it
has a cdef at the head.

However I am getting a TypeError saying "can't apply this __setattr__"
when I try to initialize an object of this type:

>>> from strlist import strlist
>>> a=strlist()
Traceback (most recent call last):
  File "<stdin>", line 1, in <module>
  File "strlist.pyx", line 24, in strlist.strlist.__init__ (strlist.c:1215)
    self.approved = False
  File "strlist.pyx", line 33, in strlist.strlist.__setattr__ (strlist.c:1417)
    super().__setattr__ ( name, value )
TypeError: can't apply this __setattr__ to strlist.strlist object

OTOH when I try the same using the pure Python implementation of the
class (i.e. just removed cdef) I have no problem:

>>> from strlist_py import strlist
>>> a=strlist()
>>> a
strlist(<super: <class 'strlist'>, <strlist object>>,approved=False)

The code is attached. Can anyone please help me figure out what I'm
doing wrong? Thanks.

-- 
Shriramana Sharma ஶ்ரீரமணஶர்மா श्रीरमणशर्मा

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if condition transformation to switch-case

Cython 0.19.1 released

Hi all,

Cython 0.19.1 is following the course of the recent 0.19 release. This is
mainly a bug fix release that adds only minor new features and fixes some
bugs and regressions in the latest release. Upgrading is generally recommended.

You can get it from here:

http://cython.org/release/Cython-0.19.1.tar.gz

http://cython.org/release/Cython-0.19.1.zip

Release notes:
https://github.com/cython/cython/blob/8f07f8d8265799cada5046fe0b7c0807d7b41fb3/CHANGES.rst

Documentation: http://docs.cython.org/

Major changes include:

* A warning is emitted when negative literal indices are found inside of
  a code section that disables ``wraparound`` handling.  This helps with
  fixing invalid code that might fail in the face of future compiler
  optimisations.

* A regression in 0.19 was fixed that rejected valid C expressions from
  being used in C array size declarations.

* Testing large (> int) C integer values for their truth value could fail
  due to integer wrap-around.

* The automatic signature documentation tries to preserve more semantics
  of default arguments and argument types.  Specifically, ``bint``
  arguments now appear as type ``bool``.

Have fun,

Stefan

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