Please write three python codes.

$1.$ How can the unique identifier, commonly referred to as the MAC or physical address, which is allocated to a computer's network interface card, be retrieved? The getnode$()$ function, found within the uuid module, is typically employed for this purpose. $(33$ Points$)$

$2.$ How can one create a Python script that initiates a process to execute the command "arp $-$a$"$ utilizing the Popen function call? $(33$ Points$)$

$3.$ Write a Python script to interpret the data within the 'mydata.txt$\text{'}$ file. Your script should convert and display the data as ASCII characters. $(34$ Points$)$