Mutability and order in Python.

Mutability and Order:

Mutability is about whether or not we can change an object once it has been created. If an object (like a list or string) can be changed (like a list can), then it is called mutable. However, if an object cannot be changed with creating a completely new object (like strings), then the object is considered immutable.

>>> my_lst = [1, 2, 3, 4, 5]
>>> my_lst[0] = 'one'
>>> print(my_lst)

 

As shown above, you are able to replace 1 with 'one' in the above list. This is because lists are mutable.

However, the following does not work:

>>> greeting = "Hello there"
>>> greeting[0] = 'M'

 

This is because strings are immutable. This means to change this string, you will need to create a completely new string.

There are two things to keep in mind for each of the data types you are using:

Are they mutable?
Are they ordered?

Order is about whether the position of an element in the object can be used to access the element. Both strings and lists are ordered. We can use the order to access parts of a list and string.

However, you will see some data types in the next sections that will be unordered. For each of the upcoming data structures you see, it is useful to understand how you index, are they mutable and are they ordered. Knowing this about the data structure is really useful!

Additionally, you will see how these each have different methods, so why you would use one data structure vs. another is largely dependent on these properties, and what you can easily do with it!