python

Python Day 4: Dictionaries

September 23, 2018 By Rowell Leave a Comment

Dictionaries

Indexes for dictionaries are called keys. Keys are associated with a value called a key-value pair. A dictionary is unordered. Compared to a List, there is no index starting at 0.

Dictionaries are typed with braces {}. To assign a dictionary to the client1 variable:

client1 = {'rssi': -52, 'channel': 36, 'noise': -96, 'tx rate': 600, 'mcs': 9}

The keys within this dictionary are rssi, channel, noise, tx rate, and mcs. The values for those keys are -52, 36, 96, 600, and 9, respectively.

To access a value through a key it is performed by:

client1[‘channel’]
36

Trying to call a key that doesn’t exist in the dictionary will result in a KeyError error message.

client1['bssid']
Traceback (most recent call last):
File "", line 1, in 
KeyError: 'bssid'

With methods, values can be returned from a dictionary. Let’s say I want to print out the key and value of client1. I’ll use a for-loop to iterate through each of the key-value pairs and print them out using the items() method.

for i in client1.items():
print(i)
('rssi', -52)
('channel', 36)
('noise', -96)
('tx rate', 600)
('mcs', 9)

If we just needed to print out the keys we would use the keys() method. Again, I’ll use the for-loop to iterate through the keys and print them out:

for k in client1.keys():
print(k)
rssi
channel
noise
tx rate
mcs

If we wanted just the values we can do the same for-loop but call the values() method:

for v in client1.values():
print(v)
-52
36
-96
600
9

Python Day 3: List Methods

September 11, 2018 By Rowell Leave a Comment

The previous day went over the basics of the Python List. On this day I go a little further into List Methods.

List Methods allow you to work with the items within a List. With methods such as removing and sorting. Useful methods when working with a list at any capacity.

Removing Values

There’s going to be a time where you need to remove a value from a list. It’s possible to do it with the del Statement.

wifi = ['rssi', 'snr', 'spatial streams']
wifi
['rssi', 'snr', 'spatial streams']
del wifi[0]
wifi
['snr', 'spatial streams']

But it is possible to do it with the remove method as well:

wifi = ['rssi', 'snr', 'spatial streams']
wifi.remove('rssi')
wifi
['snr', 'spatial streams']

The difference is the remove method uses parenthesis with the actual name of the item within the list. It’s easier to call out the actual name than the index number within the list.

But what happens if the item isn’t in the list? A ValueError occurs:

wifi.remove('antenna')
Traceback (most recent call last):
  File "<stdin>", line 1, in <module>
ValueError: list.remove(x): x not in list

Sorting Values

Let’s say I have a list of Tweeps and I want to sort it alphabetically.

tweeps = ['françois', 'robert', 'sam', 'keith', 'alex']
tweeps
['françois', 'robert', 'sam', 'keith', 'alex']
tweeps.sort()
tweeps
['alex', 'françois', 'keith', 'robert', 'sam']

Good stuff. It also works with numbers.

ages = [54, 92, 65, 27, 3]
ages.sort()
ages
[3, 27, 54, 65, 92]

What a list is not capable of sorting is a mix of integers and strings. You end up with a TypeError:

mix = ['spam', 'rice', 3, 5, 'red']
mix.sort()
Traceback (most recent call last):
  File "<stdin>", line 1, in <module>
TypeError: '<' not supported between instances of 'int' and 'str'

I’m sure in networking there will be many reasons to use a list. I can just see it happening but I don’t have any specific use case as of yet. It’s still early for me to figure out what I’d be using a list for. Maybe a list of IP addresses or interfaces of a switch or router.

Python Day 2: Lists

September 10, 2018 By Rowell Leave a Comment

Lists look like they’ll be useful when I get to a point where I can write scripts. Python Lists can hold multiple values in an ordered sequence.

Within the list are items which are ordered by an index. The index starts with 0. Each item is separated by a comma and any strings must have quotes around them.

To assign a list to a variable and retrieve an item from the list the syntax looks like:

groceries = ['oranges', 'spinach', 'eggs', 'milk']
groceries[0]
'oranges'

As I said earlier, the first value in the list starts with 0. It’s possible to go in reverse by using negative indexes:

groceries = ['oranges', 'spinach', 'eggs', 'milk']
groceries[-1]
'milk'

What if you wanted to access multiple values within a list? That’s done by slicing. A slice starts with the first integer, a colon, and the second integer is where the slice ends, but not including that item. Take a look:

groceries[0:3]
['oranges', 'spinach', 'eggs']

Modifying items within a list is possible. Let’s say you wanted to change oranges to apples in the groceries list. We need to modify index 0 within the list.

groceries[0]
'oranges'
groceries[0] = 'apples'
groceries[0]
'apples'

Removing items from a Python list is fairly simple as well by using the del statement. We must reference the index of the item we want to remove.:

groceries
['apples', 'spinach', 'eggs', 'milk']
del groceries[0]
groceries
['spinach', 'eggs', 'milk']

The items in the list move up in their index values which means spinach is now at index 0.

Adding items to the Python list is done by appending it using what’s called a method. Methods are a little different when it comes to lists because we call on the method on a value:

groceries
['spinach', 'eggs', 'milk']
groceries.append('yogurt')
groceries
['spinach', 'eggs', 'milk', 'yogurt']

By appending to the list, the new item we are adding gets added to the end of the list.

It is possible to add items to the list at a specific index. The index value must be passed, with the new item, using the insert method:

groceries
['spinach', 'eggs', 'milk', 'yogurt']
groceries.insert(0, 'pears')
groceries
['pears', 'spinach', 'eggs', 'milk', 'yogurt']

There’s quite a lot you can do with lists. They are very flexible and can be modified with ease. That’s all I’ve done with Day 2 of my Python learning exercise. The next Day will include more Python List work.

On to more practicing…

Python Day 1: Functions

September 6, 2018 By Rowell Leave a Comment

The start of my 30 Days of Code begins with Functions. I had already read about flow with For and While loops.

Today I read into Functions.

Functions are like independent programs within a program. And it is defined before it is ever called.

def myFunction():
    print('Hello world')

To utilize the function, it is called within the program or script using the function name:

myFunction()

The purpose of a function is to return a value.

Within a function, local variables can be defined. Local variables only exist (scoped) within the function and are destroyed or forgotten after the function has completed. While local variables are scoped only within the function, there is a concept of global variables.

Global variables are scoped outside of a function and can be used inside of a function. Take the example below:

def myFunction():
    global myVariable
    print('Hello ' + myVariable)

myVariable = 'Rowell'
myFunction()

The global variable statement is used inside the function but the variable is assigned outside of the function, globally. The output is as follows:

>>> myFunction()
Hello Rowell

30 Days of Code

September 6, 2018 By Rowell Leave a Comment

Anytime I get started with learning code, life seems to get in the way. I start and then I stop, I start and then I stop.

Inside of me there’s motivation but sometimes it fizzles out for one reason or another.

This time, I’m challenging myself with 30 Days of Code. A way to get me looking at Python every day for 30 days. To learn something new, type up a piece of code and run it.

It may not be the most sophisticated piece of Python code, yet.

But the purpose is for me to get in the habit of using Python regularly.

There will be short updates of my progress as I attempt to write about what I’ve learned. You can hold me accountable and correct me if I speak incorrectly.