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PYTHON setup.py build_ext --inplace
PYTHON -c "import runner"
######## setup.py ########
from Cython.Build.Dependencies import cythonize
from distutils.core import setup
# force the build order
setup(ext_modules= cythonize("foo_extension.pyx"))
setup(ext_modules = cythonize("getter*.pyx"))
######## foo_nominal.h ########
#include <Python.h>
#ifdef __cplusplus
extern "C" {
#endif
typedef struct {
PyObject_HEAD
int f0;
int f1;
int f2;
} FooStructNominal;
#ifdef __cplusplus
}
#endif
######## foo_extension.pyx ########
cdef class Foo:
cdef public int field0, field1, field2;
def __init__(self, f0, f1, f2):
self.field0 = f0
self.field1 = f1
self.field2 = f2
cdef get_field0(Foo f):
return f.field0
cdef get_field1(Foo f):
return f.field1
cdef get_field2(Foo f):
return f.field2
# A pure-python class that disallows direct access to fields
class OpaqueFoo(Foo):
@property
def field0(self):
raise AttributeError('no direct access to field0')
@property
def field1(self):
raise AttributeError('no direct access to field1')
@property
def field2(self):
raise AttributeError('no direct access to field2')
######## getter0.pyx ########
# Access base Foo fields from C via aliased field names
cdef extern from "foo_nominal.h":
ctypedef class foo_extension.Foo [object FooStructNominal]:
cdef:
int field0 "f0"
int field1 "f1"
int field2 "f2"
def sum(Foo f):
# the f.__getattr__('field0') is replaced in c by f->f0
return f.field0 + f.field1 + f.field2
######## runner.py ########
import foo_extension, getter0
foo = foo_extension.Foo(23, 123, 1023)
assert foo.field0 == 23
assert foo.field1 == 123
assert foo.field2 == 1023
ret = getter0.sum(foo)
assert ret == foo.field0 + foo.field1 + foo.field2
opaque_foo = foo_extension.OpaqueFoo(23, 123, 1023)
# C can access the fields through the aliases
opaque_ret = getter0.sum(opaque_foo)
assert opaque_ret == ret
try:
# Python cannot access the fields
f0 = opaque_ret.field0
assert False
except AttributeError as e:
pass
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