<SYSTEM_TASK:>
Solve the following problem using Python, implementing the functions described below, one line at a time
<END_TASK>
<USER_TASK:>
Description:
 def bt_addr_to_string(addr):
 """Convert a binary string to the hex representation."""

    addr_str = array.array('B', addr)
    addr_str.reverse()
    hex_str = hexlify(addr_str.tostring()).decode('ascii')
    # insert ":" seperator between the bytes
    return ':'.join(a+b for a, b in zip(hex_str[::2], hex_str[1::2]))