Python class form external module as cdef class

[Martin Bammer]

Hi,

I've got a module called MyDefs.py which contains a class like:

class FOO:
    FIRST = 1
    SECOND = 2

Now I want to import this class in another module as a cdef class, so that the cythonized looks like:

if (value == FOO->FIRST) {
...
}

How can this be done?

Best regards,

Martin

[Pierre Complex]

Hi,

cdef classes cannot inherit python classes, this is explicit in the documentation http://docs.cython.org/en/latest/src/tutorial/cdef_classes.html

Is that what you were trying to achieve? If so, maybe giving more context or motivation might help to suggest alternatives.

Regards,

Pierre

[Martin Bammer]

Hi,

no I do not want to inherit the Python class. I want to set static types, so that Cython can speedup the class member access with pure C-code.

Regards,

Martin

[Pierre Complex]

Hello,

On Wednesday, May 31, 2017 at 10:15:34 AM UTC+2, Martin Bammer wrote:

no I do not want to inherit the Python class. I want to set static types, so that Cython can speedup the class member access with pure C-code.

For this purpose, you can make the cdef class inherit from another cdef class, that is not an issue.

Given your example, you might be more interested in "enums" that can also be "cdef-ed": http://cython.readthedocs.io/en/latest/src/reference/language_basics.html?highlight=enum

Regards,

Pierre

[Robert Bradshaw]

You cannot "import" a pure Python class as a cdef class; in your example there's no underlying FOO object that provides C-level access to its members. 

If you're OK with enumerating the values, you could do

import module_containing_foo

cdef int FOO_FIRST = module_containing_foo.FOO.FIRST

cdef int FOO_SECOND = module_containing_foo.FOO.SECOND

...

cdef int value = ...

if value == FOO_FIRST:

  ...

which would get you the speed you need. (Substitute object for int if the Python "enum" has arbitrary values.)

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