cython

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"""
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Check that Cython generates a tp_clear function that actually clears object
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references to NULL instead of None.
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Discussed here: https://article.gmane.org/gmane.comp.python.cython.devel/14833
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"""
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from cpython.ref cimport PyObject, Py_TYPE
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cdef class ExtensionType:
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    """
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    Just a type which is handled by a specific C type (instead of PyObject)
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    to check that tp_clear works when the C pointer is of a type different
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    from PyObject *.
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    """
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# Pull tp_clear for PyTypeObject as I did not find another way to access it
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# from Cython code.
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cdef extern from "Python.h":
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    ctypedef struct PyTypeObject:
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        void (*tp_clear)(object)
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cdef class TpClearFixture:
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    """
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    An extension type that has a tp_clear method generated to test that it
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    actually clears the references to NULL.
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    >>> fixture = TpClearFixture()
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    >>> isinstance(fixture.extension_type, ExtensionType)
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    True
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    >>> isinstance(fixture.any_object, str)
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    True
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    >>> fixture.call_tp_clear()
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    >>> fixture.check_any_object_status()
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    'NULL'
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    >>> fixture.check_extension_type_status()
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    'NULL'
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    """
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    cdef readonly object any_object
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    cdef readonly ExtensionType extension_type
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    def __cinit__(self):
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        self.any_object = "Hello World"
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        self.extension_type = ExtensionType()
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    def call_tp_clear(self):
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        cdef PyTypeObject *pto = Py_TYPE(self)
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        pto.tp_clear(self)
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    def check_any_object_status(self):
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        if <void*>(self.any_object) == NULL:
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            return 'NULL'
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        elif self.any_object is None:
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            return 'None' 
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        else:
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            return 'not cleared'
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    def check_extension_type_status(self):
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        if <void*>(self.any_object) == NULL:
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            return 'NULL'
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        elif self.any_object is None:
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            return 'None' 
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        else:
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            return 'not cleared'
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