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# Python Set and Frozenset

## What is `Set` and `frozenset`?

In our previous Data Types lesson, we divided the data types in Python into mutable (Mutable) and immutable (unchangeable) and here we will process both mutable and immutable data types.

`Dictionaries` are a little different because `Dictionaries` consist of two parts; `keys` and `values`, value part can contain all data type but keys part can only be of `string` and `int` type.

## What is `Set`?

It is a data type that contains multiple data types such as list, dictionary, and tuple data types. You can perform all kinds of functions (joining, intersection, etc.) related to sets with this data type.

## `Set` Usage

Let me show you the use of `set` with an example;

``````set = {"Python", 'b', 5, "Baransel"}
``````

It has a very simple usage, but there is something we should pay attention to here if we define an empty set as follows;

``````set = {}
``````

The interpreter will detect it as a `Dictionary`. Well, if you ask how to create an empty set, let me show you;

``````set = set()
``````

we define as.

Let me give another important note about sets: there can be only one element from an element, just like the sets we see here in mathematics. Well, let's see what happens if we try to add;

``````set = {"Python", 'b', 5, "Baransel", "Python"}

print(set)
# {"Python", 'b', 5, "Baransel"}
``````

Now you will say ok, but we added it, it didn't make any mistakes, but if you say it shows only one of the same ones while showing, let me show you as follows.

``````set = {"Python", 'b', 5, "Baransel", "Python"}
print(len(set))
# 4
``````

As you can see, when we look at the length of the set, the set sees 4 elements even though we add 5 elements. Since we have given this important note, let me show you how we access the elements of the `Set`.

### Accessing `Set` Items

``````set = {"Python", 'b', 5, "Baransel", "Python"}
print(set[3])

# TypeError: 'set' object does not support indexing
``````

We got an error in this way because `Set` is not an ordered data type like Dictionaries. So it does not support indexing. Now you will say, why should I use sets, it is true, although the sets seem unnecessary on their own, you will need them when there is more than one `set`, then you will see how necessary the sets are. That's why I immediately switch to `Set` Method.

Let's show the `set` methods with the `dir()` function as in every lesson.

### `Set` Methods

``````['__and__', '__class__', '__contains__', '__delattr__', '__dir__', '__doc__',
'__eq__', '__format__', '__ge__', '__getattribute__', '__gt__', '__hash__',
'__iand__', '__init__', '__ior__', '__isub__', '__iter__', '__ixor__',
'__le__', '__len__', '__lt__', '__ne__', '__new__', '__or__', '__rand__',
'__reduce__', '__reduce_ex__', '__repr__', '__ror__', '__rsub__', '__rxor__',
'__setattr__', '__sizeof__', '__str__', '__sub__', '__subclasshook__', '__xor__',
'intersection', 'intersection_update', 'isdisjoint', 'issubset', 'issuperset',
'pop', 'remove', 'symmetric_difference', 'symmetric_difference_update', 'union',
'update']
``````

In this lesson, as in other lessons, we will not go into `__X__` methods, that is, special methods.

``````['add', 'clear', 'copy', 'difference', 'difference_update', 'discard',
'intersection', 'intersection_update', 'isdisjoint', 'issubset', 'issuperset',
'pop', 'remove', 'symmetric_difference', 'symmetric_difference_update', 'union',
'update']
``````

### `add` Method

Continue this post on my blog! Python Set and Frozenset.