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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 _unpack(formatstring, packed):
 """Unpack a bytestring into a value. Uses the built-in :mod:`struct` Python module. Args: * formatstring (str):
 String for the packing. See the :mod:`struct` module for details. * packed (str):
 The bytestring to be unpacked. Returns: A value. The type depends on the formatstring. Raises: ValueError Note that the :mod:`struct` module wants byte buffers for Python3, but bytestrings for Python2. This is compensated for automatically. """

    _checkString(formatstring, description='formatstring', minlength=1)
    _checkString(packed, description='packed string', minlength=1)

    if sys.version_info[0] > 2:
        packed = bytes(packed, encoding='latin1')  # Convert types to make it Python3 compatible

    try:
        value = struct.unpack(formatstring, packed)[0]
    except:
        errortext = 'The received bytestring is probably wrong, as the bytestring-to-num conversion failed.'
        errortext += ' Bytestring: {0!r} Struct format code is: {1}'
        raise ValueError(errortext.format(packed, formatstring))

    return value