## Binary

Binary is nothing more than a base 2 numbering system using the numbers 0 and 1.

### Bit

A Bit is merely a single number of either 1 and 0 within the binary.

### Byte

A Byte consists of 8 bits. A byte containing all 0s will be the integer 0, while a byte containing all 1s will be the integer of 255.

### Nibble

A Nibble consits of 4 bits. A nibble containing all 0s will be the iteger 0, while a nibble containing all 1s will be the integer 15 (very useful for hex numbers).

## Python code

What I want to do is write a Python class for taking a valid byte (number from 0 – 255), and get its binary representation. I would also like to get the high nibble and low nibble from that binary.

### Constructor

Lets start by making a constructor and verifying we have a valid byte.

class Byte(object):
"""Do cool things with a 8 bit number"""

def __init__(self, number):
if not self.__isbyte(number):
raise Exception('"%s" is not a 8 bit integer' % number)
self.number = number

def __isint(self, number):
"""Check if a input is of type int"""
if type(number) == int:
return True

def __isbyte(self, number):
"""Check if a input is a byte, 0 - 255"""
if self.__isint(number):
if len(bin(number)[2:]) <= 8:
return True

Alright, this code will let us define a object and verify it is a 8 bit integer.

### Binary Representation

Next lets create the pretty binary representation with leading 0s as padding.

def __format(self, num, size=8):
"""Format a number as binary with leading zeros"""
return str(bin(num)[2:]).zfill(size)

@property
def binary(self):
"""Return Byte in binary"""
return self.__format(self.number)

Here I wrote a small helper function for extracting the binary representation from the bin function and stripped the leading 0b. The binary property will return the binary.

### High Nibble

Being all bytes are 8 bits, we can be sure a byte will have a high nibble (first 4 bits), and a low nibble (last 4 bits).

In order to get our high nibble all we need to do is use the bitwise right shift operator.

def __high_nibble(self):
"""Use Bitwise shift to get high nibble from byte"""
return self.number >> 4

@property
def high_nibble(self):
"""Return High Nibble in binary"""
return self.__format(self.__high_nibble(), 4)

### Low Nibble

In order to get our low nibble we can use the bitwise AND operator with a mask of 15 (remember 15 is a nibble of all 1s).

def __low_nibble(self):
"""Use Bitwise AND to get low nibble"""
return self.number & 0x0F  # 0x0F == 15

@property
def low_nibble(self):
"""Return Low Nibble in binary"""
return self.__format(self.__low_nibble(), 4)

### Code in action

There you have it, lets go ahead and give it a try.

In [1]: myByte = Byte(15)

In [2]: myByte.binary
Out[2]: '00001111'

In [3]: myByte.high_nibble
Out[3]: '0000'

In [4]: myByte.low_nibble
Out[4]: '1111'

## Working with Libvirt using Python

Today I decide to toy around with a KVM server we have running in house for testing. I started by using the libvirt Documentation, but it was very limited and I had to do some trial and error. I will go over a few basic things I learned using the libvirt Python module:

Normally we us virt-manager to connect to our KVM instances, and the authentication is tunnled over SSH (using SSH Keys) and QEMU. First things first I had to learn how to connect with the same method we used in virt-manager:

>>> import libvirt
>>> conn = libvirt.open("qemu+ssh://root@192.168.1.2/system")
>>> conn
<libvirt.virConnect instance at 0x2b518c0>

Using the open function I was able to successfully connect to our Hypervisor:

>>> conn.getHostname()
'kvm01.company.com'

From here I need only see our running virtual machines, and how to interact with them. I noticed two separate function the listDefinedDomains() and listDomainsID().

These two functions do two separate things, first lets go over listDefinedDomains(), this function will return a list of offline guest by name:

>>> conn.listDefinedDomains()
['rawhide', 'el4-i386', 'el5-64', 'el6-64', ....]

Where as listDomainsID() will return a list of online devices by ID:

>>> conn.listDomainsID()
[1, 2, 10, 3, 17, 7, 9, 8, 5, 6]

Once connected to the Domain you can get its name:

>>> for i in conn.listDomainsID():
...     print conn.lookupByID(i).name()
...
...
build01-dev
data01-dev
build02-dev
CentOS6-x86_64-dev
..

And as you would expect you can connect to either offline or online domains by using their name:

>>> dom = conn.lookupByName('build01-dev')
>>> dom
<libvirt.virDomain instance at 0x2b82c68>
>>> dom.name()
'build01-dev'

Now that we understand the process of connecting to our Hypervisor and parsing our Domains, lets go over how to start and stop these Domains, or as libvirt calls it create and destroy.

Lets start out with a offline (or destroyed) domain:

>>> dom = conn.lookupByName('rawhide')
>>> dom.isActive()
0

To bring this Domain online we need to use the create() function:

>>> dom.create()
0
>>> dom.isActive()
1

And to power it down you would destroy() it:

>>> dom.destroy()
0
>>> dom.isActive()
0

I hope this helped out a few of you out there, I know this was rather confusion when I first started messing around with it.