cython

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"""
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Check that the @cython.no_gc decorator disables generation of the
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tp_clear and tp_traverse slots, that is, disables cycle collection.
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"""
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cimport cython
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from cpython.ref cimport PyObject, Py_TYPE
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# Force non-gc'd PyTypeObject when safety is guaranteed by user but not provable
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cdef extern from *:
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    ctypedef struct PyTypeObject:
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        void (*tp_clear)(object)
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        void (*tp_traverse)(object)
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def is_tp_clear_null(obj):
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    return (<PyTypeObject*>Py_TYPE(obj)).tp_clear is NULL
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def is_tp_traverse_null(obj):
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    return (<PyTypeObject*>Py_TYPE(obj)).tp_traverse is NULL
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@cython.no_gc
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cdef class DisableGC:
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    """
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    An extension type that has tp_clear and tp_traverse methods generated 
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    to test that it actually clears the references to NULL.
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    >>> uut = DisableGC()
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    >>> is_tp_clear_null(uut)
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    True
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    >>> is_tp_traverse_null(uut)
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    True
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    """
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    cdef public object requires_cleanup
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    def __cinit__(self):
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        self.requires_cleanup = (
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                "Tuples to strings don't really need cleanup, cannot take part of cycles",)
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