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r'''
This tests the '_objects' attribute of ctypes instances. '_objects'
holds references to objects that must be kept alive as long as the
ctypes instance, to make sure that the memory buffer is valid.
WARNING: The '_objects' attribute is exposed ONLY for debugging ctypes itself,
it MUST NEVER BE MODIFIED!
'_objects' is initialized to a dictionary on first use, before that it
is None.
Here is an array of string pointers:
>>> from ctypes import *
>>> array = (c_char_p * 5)()
>>> print(array._objects)
None
>>>
The memory block stores pointers to strings, and the strings itself
assigned from Python must be kept.
>>> array[4] = b'foo bar'
>>> array._objects
{'4': b'foo bar'}
>>> array[4]
b'foo bar'
>>>
It gets more complicated when the ctypes instance itself is contained
in a 'base' object.
>>> class X(Structure):
... _fields_ = [("x", c_int), ("y", c_int), ("array", c_char_p * 5)]
...
>>> x = X()
>>> print(x._objects)
None
>>>
The'array' attribute of the 'x' object shares part of the memory buffer
of 'x' ('_b_base_' is either None, or the root object owning the memory block):
>>> print(x.array._b_base_) # doctest: +ELLIPSIS
<ctypes.test.test_objects.X object at 0x...>
>>>
>>> x.array[0] = b'spam spam spam'
>>> x._objects
{'0:2': b'spam spam spam'}
>>> x.array._b_base_._objects
{'0:2': b'spam spam spam'}
>>>
'''
import unittest, doctest
import ctypes.test.test_objects
class TestCase(unittest.TestCase):
def test(self):
failures, tests = doctest.testmod(ctypes.test.test_objects)
self.assertFalse(failures, 'doctests failed, see output above')
if __name__ == '__main__':
doctest.testmod(ctypes.test.test_objects)