Byte arrays and DLLs

[Eryk Sun]

On 6/30/22, Rob Cliffe via Python-list <python-list at python.org> wrote:
>
> AKAIK it is not possible to give ctypes a bytearray object and persuade
> it to give you a pointer to the actual array data, suitable for passing
> to a DLL.

You're overlooking the from_buffer() method. For example:

    >>> ba = bytearray(10)
    >>> ca = (ctypes.c_char * len(ba)).from_buffer(ba)
    >>> ca.value = b'spam&eggs'
    >>> ba
    bytearray(b'spam&eggs\x00')

Note that the bytearray can't be resized while a view of the data is
exported. For example:

    >>> ba.append(97)
    Traceback (most recent call last):
      File "<stdin>", line 1, in <module>
    BufferError: Existing exports of data: object cannot be re-sized

    >>> del ba[-1]
    Traceback (most recent call last):
      File "<stdin>", line 1, in <module>
    BufferError: Existing exports of data: object cannot be re-sized