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Per-instance extra scope variables

  • Author: DagSverreSeljebotn
  • Status: Idea

NOT DONE!, only draft, I got another idea... :-)

The reason for this madness

To access NumPy arrays, strides must be looked up and divided by the datatype size. I can see three :
  • A custom parse tree translation for NumPy (whether pluggable in by a plugin, specified in pxd, or otherwise)
  • A simple approach of

This can mostly be considered a hack.

, in order to be able to implement [:enhancements/operators/ambitious] for NumPy arrays without expecting too complex optimizations of the Cython compiler. The full NumPy problem will be described at the bottom, but the spec comes first.

Please be patient and you'll hopefully see why at the bottom...

Description

This is done:
  • A new scopevars block can be defined on a type (in pxd or pyx, not sure)
  • The variables in this block is instantiated in the local scope
  • Variables in the block can be accessed using the scope() function from within the class, and any method calling scope() must be inlined by the Cython compiler.

To allow a scopevars block within a cdef class:

.pxd:

ctypedef class Foo:
    char* complex_buffer

    scopevars:
        int info

.pyx:

cdef class Foo:
    def __enterscope__(self):
        scope(self).info = self.complex_buffer[34] // 4

    def bar(self): print scope(self).info

When using this type now, the following happens:

Foo f = ...
f.info()

is transformed by the ScopeVarsTransformer to:

Foo f = ...
int _scopetmp_f_info
_scopetmp_f_info = f.complex_buffer[34] // 34
print _scopetmp_f_info

Why?

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