import unittest
from ctypes import *

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

class 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 = "foo"
        c2 = cell()
        c2.name = "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]
        assert result == ["foo", "bar"] * 4

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