Working with Lists of Python for Network Engineers

This post is about the most common / useful things we do with Lists in Python.

Iterating over Lists

Most of the time we use FOR loops to iterate over Lists as it can do things for all the items in a List easily.

As an example, printing all values in a List can be done by the following code.

The result will be;

Another example will be to find the data types of the items in a List like the following,

The result will be;

Indexing, Counting & Slicing

This way we can target the items in a List instead of looping for all items.

You can see that the indexing starts with 0 and if given a negative value, it will start reading from the end.

0th item is "vlan5" and -1th item is "vlan15".

Len() function will tell you how many items are there..

count() function will tell you how many items are there of a specific value.

We can slice the List like the following,

list[X,Y] 

As you can see, Xth item is included and Yth item is excluded.

How about the following,

This means that the slicing starts with the 2nd item (note that 2nd item means actually the 3rd item as it starts from 0) and ends with 6th item (7th) but it will only capture with a gap of 1 (every second item)

Min & Max Functions

These functions help us to get the minimum and maximum values in the List items depending on the data type. As an example, if the List is full of numbers;

Let's see what happens when they are Strings..

It did not captured the item with the minimum / maximum number of characters instead it captured the lowest and highest ASCII character in order. "b" comes 1st than "i" or "l".

You can see as the Capital Letters comes 1st, it captured "Indonesia" this time. Let's see what happens if the numbers are put in string format.

But note that you cannot use min and max functions when the data types are mixed.

Appending, Inserting and Extending

append() function adds an item to the end of the List while insert() function inserts an item to a position you want and extend() function adds multiple items to the List. But there is a rule in using extend() function and that is you have to use an item which can be iterated means which can be run through a loop like FOR loop. Examples are another list or an String..

As you can see it adds the items to the end, let's see what will happen if we try to add an item to the list directly which means we try to use extend() function like the append() function.

It was taken as a String..

Let's see a real world example using the things so far..

Above program inspects all items in the list "ip_addresses" and put in to the list "public_ips" if those items does not contain the characters "192.168".

Popping, Removing and Clearing

pop() function can be used to remove an item from a List targeting an exact position of an item. However if the position is not specified, it will remove the last item of the list.

remove() function will be useful when you need to remove an item by the value. But it if duplicate values are there, it will only remove the 1st item it finds in the list.

Sorting Lists

sort() function comes handy when you needs to sort the values of the items in a List. This just works like the min() and max () functions as if all the items are numbers, it will sort normally and if the items are strings, it will again do the sorting based on the ASCII order.

Nested Lists

We can put a List inside of another List.

You can access the individual values of the nested List like the following..

Note:-

Since Tuples are very much same as Lists, but being immutable, some of the above functions like min(), max(), len(), count() also works with Tuples.