如何在使用ctypes.pythonapi.PyCapsule_New时设置名称参数

Question

如何通过ctypes将胶囊的名称传入PyCapsule_New的第二个参数

我尝试过以下方法，但似乎有问题：

capsule = ctypes.pythonapi.PyCapsule_New(b'data', b'abcdef.ghijkl', None)
capsule = ctypes.pythonapi.PyCapsule_New(b'data', ctypes.create_string_buffer(b"abcdef.ghijkl"), None)
capsule = ctypes.pythonapi.PyCapsule_New(b'data', ctypes.c_chap_p(b"abcdef.ghijkl"), None)

例如，胶囊的名称设置不正确：

>>> import ctypes
>>> ctypes.pythonapi.PyCapsule_New.argtypes = [ctypes.c_void_p, ctypes.c_char_p, ctypes.c_void_p]
>>> ctypes.pythonapi.PyCapsule_New.restype = ctypes.py_object
>>>
>>> capsule = ctypes.pythonapi.PyCapsule_New(b'data', b'abcdef.ghijkl', None)
>>>
>>> capsule
<capsule object "" at 0xf7102f98>
>>> capsule
<capsule object "e" at 0xf7102f98>
>>> capsule
<capsule object "���capsule
<capsule object "" at 0xf7102f98>
>>> capsule
<capsule object "e" at 0xf7102f98>
>>> capsule
<capsule object "e" at 0xf7102f98>
>>> capsule
<capsule object "���

如果我使用ctypes.create_string_buffer(b"abcdef.ghijkl")

>>> capsule = ctypes.pythonapi.PyCapsule_New(b'data', ctypes.create_string_buffer(b"abcdef.ghijkl"), None)
>>> capsule
<capsule object "abcdef.ghijkl" at 0xf7102fb0>
>>> capsule
<capsule object "" at 0xf7102fb0>
>>> capsule
<capsule object "" at 0xf7102fb0>
>>> capsule
<capsule object "" at 0xf7102fb0>
>>> capsule
<capsule object "" at 0xf7102fb0>

这里奇怪的是，如果我做了一个返回胶囊的C扩展，我可以使用ctype提取它的名称，并且它可以工作：

>>> capsule_from_c_ext = mycext.capsule()
>>> ctypes.pythonapi.PyCapsule_GetName.restype = ctypes.c_char_p
>>> ctypes.pythonapi.PyCapsule_GetName.argtypes = [ctypes.py_object]
>>> name = ctypes.pythonapi.PyCapsule_GetName(capsule_from_c_ext)
>>> name
b"abcdef.ghijkl"
>>> type(name)
<class 'bytes'>
>>> assert name == b"abcdef.ghijkl"
>>>
>>> capsule = ctypes.pythonapi.PyCapsule_New(b'data', name, None)
>>> capsule
<capsule object "abcdef.ghijkl" at 0xf6f23c20>
>>> capsule
<capsule object "abcdef.ghijkl" at 0xf6f23c20>
>>> capsule
<capsule object "abcdef.ghijkl" at 0xf6f23c20>
>>>
>>> capsule
<capsule object "abcdef.ghijkl" at 0xf6f23c20>
>>> capsule
<capsule object "abcdef.ghijkl" at 0xf6f23c20>

此外，如果您使用一个较短的名称，如b'name'，它似乎可以正常工作。

Answer 1

我从docs得到了一个提示

名称字符串可以是NULL，也可以是指向有效C字符串的指针。如果不为空，此字符串的存留时间必须大于胶囊。(尽管允许它在析构函数中释放它。)

首先创建一个名为的变量，然后调用它，似乎是可行的：

>>> import ctypes
>>> ctypes.pythonapi.PyCapsule_New.argtypes = [ctypes.c_void_p, ctypes.c_char_p, ctypes.c_void_p]
>>> ctypes.pythonapi.PyCapsule_New.restype = ctypes.py_object
>>> name = b'abcdef.ghijkl'
>>> capsule = ctypes.pythonapi.PyCapsule_New(b'data', name, None)
>>>
>>> capsule
<capsule object "abcdef.ghijkl" at 0xf6f23bd8>
>>> capsule
<capsule object "abcdef.ghijkl" at 0xf6f23bd8>
>>> capsule
<capsule object "abcdef.ghijkl" at 0xf6f23bd8>
>>> capsule
<capsule object "abcdef.ghijkl" at 0xf6f23bd8>

并且您可以证明您需要name变量不被释放：

del name
>>> capsule
<capsule object "" at 0xf7102fb0>
>>> capsule
<capsule object "" at 0xf7102fb0>
>>> capsule
<capsule object "" at 0xf7102fb0>
>>> capsule
<capsule object "" at 0xf7102fb0>