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# Requiere instalar netifaces
import netifaces

def mac_for_ip(ip):
    """
    Returns a list of MACs for interfaces that have given IP, returns None if not found
    :param ip: string
    :return: if_mac|None: ip + mac
    """
    for i in netifaces.interfaces():
        addrs = netifaces.ifaddresses(i)
        try:
            if_mac = addrs[netifaces.AF_LINK][0]['addr']
            if_ip = addrs[netifaces.AF_INET][0]['addr']
        except (IndexError, KeyError): # ignore ifaces that dont have MAC or IP
            if_mac = if_ip = None
        if if_ip == ip:
            return if_mac
    return None


ip = '192.168.1.100'

print(mac_for_ip(ip))
# 50:a1:47:0c:ed:d8