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Solve the following problem using Python, implementing the functions described below, one line at a time
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Description:
 def _decoder(image, shrink):
 """A context manager for `DmtxDecode`, created and destroyed by `dmtxDecodeCreate` and `dmtxDecodeDestroy`. Args: image (POINTER(DmtxImage)):
 shrink (int):
 Yields: POINTER(DmtxDecode):
 The created decoder Raises: PyLibDMTXError: If the decoder could not be created. """

    decoder = dmtxDecodeCreate(image, shrink)
    if not decoder:
        raise PyLibDMTXError('Could not create decoder')
    else:
        try:
            yield decoder
        finally:
            dmtxDecodeDestroy(byref(decoder))