convert python object to cython pointer
cython
Solution
I found the solution. You have to tell cython that foo._impl is really cFoo* instance. That can be achieved by providing Foo definition (e.g. in foo.pxd). Afterwards you are able to cast python object to Foo and cython will know that its _impl field has type cFoo*.
foo.pxd
from c_foo cimport cFoo
cdef class Foo:
cdef cFoo* _impl
foo.pyx
from c_foo cimport cFoo
cdef class Foo:
# methods implementation
c_foo_holder.pxd
cdef extern from "FooHolder.h":
cdef cppclass cFooHolder:
cFooHolder(cFoo* foo)
foo_holder.pyx
from c_foo_holder cimport cFooHolder
from c_foo cimport cFoo
from foo cimport Foo
cdef class FooHolder:
cdef cFooHolder* _impl
def __init__(self, foo):
self._impl = new cFooHolder((<Foo?>foo)._impl)
Problem
I'm trying to expose c++ classes to python using cython. I wrote their definitions in *.pxd file and implemented a wrappers in *.pyx files. But I got stuck trying to pass to a function pointer to the extension type. Here is simplified example. foo.pyx ``` from c_foo cimport cFoo cdef class Foo: cdef cFoo* _impl ``` c_foo_holder.pxd ``` cdef extern from "FooHolder.h": cdef cppclass cFooHolder: cFooHolder(cFoo* foo) ``` foo_holder.pyx ``` from c_foo_holder cimport cFooHolder from c_foo cimport cFoo cdef class FooHolder: cdef cFooHolder* _impl def __init__(self, foo): self._impl = new cFooHolder(<cFoo*>(foo._impl)) # error here ``` But on the last line I get error "Python objects cannot be cast to pointers of primitive types". I also tried several other approaches, but nothing worked: ``` # error: 'Foo' is not a type identifier from foo import Foo def __init__(self, Foo foo): self._impl = new cFooHolder(foo._impl) # error: 'Foo' is not a type identifier def __init__(self, foo): self._impl = new cFooHolder(<Foo>(foo)._impl) ```