Eryk Sun added the comment:
If your goal is to get a bytes object, I don't see the point of creating an
array. string_at is simpler and more efficient.
If you really must create an array, note that simple pointers (c_void_p,
c_char_p, c_wchar_p) need special handling. They don't have a `contents`
attribute, and their _type_ is a string.
Also, I think combining from_address and addressof is a bit convoluted. I think
it's cleaner to implement this using an array pointer:
>>> ptr = POINTER(c_int)((c_int * 3)(1,2,3))
>>> arr = POINTER(ptr._type_ * 3)(ptr.contents)[0]
>>> arr[:]
[1, 2, 3]
This also keeps the underlying ctypes object(s) properly referenced:
>>> arr._b_base_
<__main__.LP_c_int_Array_3 object at 0x7fb28471cd90>
>>> arr._b_base_._objects['0']['1']
<__main__.c_int_Array_3 object at 0x7fb28477da60>
whereas using from_address creates an array that dangerously doesn't own its
own data and doesn't keep a reference to the owner:
>>> arr2 = (ptr._type_ * 3).from_address(addressof(ptr.contents))
>>> arr2._b_needsfree_
0
>>> arr2._b_base_ is None
True
>>> arr2._objects is None
True
Let's create a larger array to ensure it's using an mmap region instead of the
heap. This ensures a segfault when trying to access the memory block after it's
deallocated:
>>> ptr = POINTER(c_int)((c_int * 100000)(*range(100000)))
>>> arr = (ptr._type_ * 100000).from_address(addressof(ptr.contents))
>>> del ptr
>>> x = arr[:]
Segmentation fault (core dumped)
whereas using a dereferenced array pointer keeps the source data alive:
>>> ptr = POINTER(c_int)((c_int * 100000)(*range(100000)))
>>> arr = POINTER(ptr._type_ * 100000)(ptr.contents)[0]
>>> del ptr
>>> x = arr[:]
>>> x[-5:]
[99995, 99996, 99997, 99998, 99999]
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<http://bugs.python.org/issue27274>
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