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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 bin_to_mac(bin, size=6):
 """Convert 6 bytes into a MAC string. Args: bin (str):
 hex string of lenth 6. Returns: str: String representation of the MAC address in lower case. Raises: Exception: if ``len(bin)`` is not 6. """

    if len(bin) != size:
        raise Exception("Invalid MAC address: %s" % (bin))
    return ':'.join([binascii.hexlify(o) for o in bin])