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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 read_flash(self, addr=0xFF, page=0x00):
 """Read back a flash page from the Crazyflie and return it"""

        buff = bytearray()

        page_size = self.targets[addr].page_size

        for i in range(0, int(math.ceil(page_size / 25.0))):
            pk = None
            retry_counter = 5
            while ((not pk or pk.header != 0xFF or
                    struct.unpack('<BB', pk.data[0:2]) != (addr, 0x1C)) and
                    retry_counter >= 0):
                pk = CRTPPacket()
                pk.set_header(0xFF, 0xFF)
                pk.data = struct.pack('<BBHH', addr, 0x1C, page, (i * 25))
                self.link.send_packet(pk)

                pk = self.link.receive_packet(1)
                retry_counter -= 1
            if (retry_counter < 0):
                return None
            else:
                buff += pk.data[6:]

        # For some reason we get one byte extra here...
        return buff[0:page_size]