An Internet Service Provider $($ISP$)$ must, as part of its service to customers, provide a Domain Name Server $($DNS$).$

A DNS is a server that maintains a database of domain names, such as www$.$griffith.edu.au$,$ and their corresponding Internet Protocol Addresses $($IPA$),$ such as $132\mathrm{.}234\mathrm{.}243\mathrm{.}22.$ A domain name has only one IPA, but an IPA may have many domain names. $88\mathrm{.}88\mathrm{.}0\mathrm{.}0$

Define a class that simulates a DNS$.$ It must have:

$$ a method for updating the DNS with a new domain name and its IPA;

$$ a method for returning the IPA for a domain name, or None if it does not exist; and

$$ whatever private attributes are required to support the methods.

Write a test program that allows the user to test the class, by typing in fake domain names and IPAs to update the DNS$,$ and domain names to look up$.$ An example of the output from the test program is like this:

$?$ u www$.$google.com $8\mathrm{.}8\mathrm{.}8\mathrm{.}8$

$?$ u www$.$amazon.com $2\mathrm{.}2\mathrm{.}2\mathrm{.}2$

$?$ u www$.$cnn$.$com

Bad command.

$?$ l www$.$google.com

$8\mathrm{.}8\mathrm{.}8\mathrm{.}8$

$?$ l www$.$amazon.com

$2\mathrm{.}2\mathrm{.}2\mathrm{.}2$

$?$ l www$.$cnn$.$com

None

$?$ q

where:

$$ u DNS IPA updates the DNS with a new domain name and its IPA;

$$ l DNS returns the IPA for a domain name, or None if it does not exist; and

$$ q ends the test program.

Bad inputs are to be reported and ignored.