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//usr/local/lib/python3.9/ctypes/test/test_incomplete.py

import unittest
from ctypes import *

################################################################
#
# The incomplete pointer example from the tutorial
#

class MyTestCase(unittest.TestCase):

def test_incomplete_example(self):
        lpcell = POINTER("cell")
        class cell(Structure):
            _fields_ = [("name", c_char_p),
                        ("next", lpcell)]

SetPointerType(lpcell, cell)

c1 = cell()
        c1.name = b"foo"
        c2 = cell()
        c2.name = b"bar"

c1.next = pointer(c2)
        c2.next = pointer(c1)

p = c1

result = []
        for i in range(8):
            result.append(p.name)
            p = p.next[0]
        self.assertEqual(result, [b"foo", b"bar"] * 4)

# to not leak references, we must clean _pointer_type_cache
        from ctypes import _pointer_type_cache
        del _pointer_type_cache[cell]

################################################################

if __name__ == '__main__':
    unittest.main()