Data Structures

Related with data structures

Data Structures

Data structures are containers that organize and group data types together in different ways.

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.

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.

List

A list is one of the most common and basic data structures in Python. List are Mutable and ordinated data structures

list_of_random_things = [1, 3.4, 'a string', True]

Tuples

Tuples are a data type for immutable ordered sequences of elements. They are often used to store related pieces of information, tuples are immutable - you can't add and remove items from tuples, or sort them in place

location = (13.4125, 103.866667)

Tuples can also be used to assign multiple variables in a compact way. In the example bellow, a tuple called dimensions is created, next, the content of this tuple is unpack, in three different variables, this is called tuple unpacking.

dimensions = 52, 40, 100
length, width, height = dimensions

The parentheses are optional when defining tuples, and programmers frequently omit them if parentheses don't clarify the code.

Set

A set is a data type for mutable unordered collections of unique elements. One application of a set is to quickly remove duplicates from a list, it is an unordered data type, there fore if the method .pop() is use there is no way to know exactly with element will be eliminated.

numbers = [1, 2, 6, 3, 1, 1, 6]
unique_nums = set(numbers)
print(unique_nums)

It will output:

{1, 2, 3, 6}

Dictionaries

A dictionary is a mutable data type that stores mappings of unique keys to values.

elements = {"hydrogen": 1, "helium": 2, "carbon": 6}

Dictionaries can have keys of any immutable type, like integers or tuples, not just strings. It's not even necessary for every key to have the same type.

If you expect lookups to sometimes fail, get might be a better tool than normal square bracket lookups because errors can crash your program.

print("carbon" in elements)
print(elements.get("dilithium"))

this would output:

True
None

So, to recap

Data Structure	Ordered	Mutable	Constructor	Example
List	Yes	Yes	[] or list()	[5.7,4,'yesy',5.7]
Tuple	Yes	No	() or tuple()	(5.7,4,'yes',5.7)
Set	No	Yes	{}1 or set()	{5.7,4,'yes'}
Dictionary	No	No2	{} or dict()	{'jun':75.'jul':89}

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1. You can use curly braces to define a set like this: {1, 2, 3}. However, if you leave the curly braces empty like this: {} Python will instead create an empty dictionary. So to create an empty set, use set(). ↩

2. A dictionary itself is mutable, but each of its individual keys must be immutable. ↩