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import cython
from cython.cimports.libc.stdlib import malloc, free
# Example C struct
my_c_struct = cython.struct(
a = cython.int,
b = cython.int,
)
@cython.cclass
class WrapperClass:
"""A wrapper class for a C/C++ data structure"""
_ptr: cython.pointer(my_c_struct)
ptr_owner: cython.bint
def __cinit__(self):
self.ptr_owner = False
def __dealloc__(self):
# De-allocate if not null and flag is set
if self._ptr is not cython.NULL and self.ptr_owner is True:
free(self._ptr)
self._ptr = cython.NULL
def __init__(self):
# Prevent accidental instantiation from normal Python code
# since we cannot pass a struct pointer into a Python constructor.
raise TypeError("This class cannot be instantiated directly.")
# Extension class properties
@property
def a(self):
return self._ptr.a if self._ptr is not cython.NULL else None
@property
def b(self):
return self._ptr.b if self._ptr is not cython.NULL else None
@staticmethod
@cython.cfunc
def from_ptr(_ptr: cython.pointer(my_c_struct), owner: cython.bint=False) -> WrapperClass:
"""Factory function to create WrapperClass objects from
given my_c_struct pointer.
Setting ``owner`` flag to ``True`` causes
the extension type to ``free`` the structure pointed to by ``_ptr``
when the wrapper object is deallocated."""
# Fast call to __new__() that bypasses the __init__() constructor.
wrapper: WrapperClass = WrapperClass.__new__(WrapperClass)
wrapper._ptr = _ptr
wrapper.ptr_owner = owner
return wrapper
@staticmethod
@cython.cfunc
def new_struct() -> WrapperClass:
"""Factory function to create WrapperClass objects with
newly allocated my_c_struct"""
_ptr: cython.pointer(my_c_struct) = cython.cast(
cython.pointer(my_c_struct), malloc(cython.sizeof(my_c_struct)))
if _ptr is cython.NULL:
raise MemoryError
_ptr.a = 0
_ptr.b = 0
return WrapperClass.from_ptr(_ptr, owner=True)
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