Returns unpacked Python struct array.

        Args:
            offset (int): offset to byte array within structure
            length (int): how many bytes to unpack
            format (str): Python struct format string for unpacking

        See Also:
            https://docs.python.org/2/library/struct.html#format-characters

def get_field(self, offset, length, format):
        """Returns unpacked Python struct array.

        Args:
            offset (int): offset to byte array within structure
            length (int): how many bytes to unpack
            format (str): Python struct format string for unpacking

        See Also:
            https://docs.python.org/2/library/struct.html#format-characters
        """
        return struct.unpack(format, self.data[offset:offset + length])[0]