Sets and Frozen Sets are built-in data types in Python. Both of them are unordered datatypes used to store distinct elements. If you have worked with a different programming language, you might be familiar with Set. However, Frozen Sets are not so common and unique to Python. The biggest advantage of a set and frozen set are the fact that they have a lookup time of O(1).
Frozen Sets are built on top of Sets and as a result, they have many similarities.
A quick summary of their similarities and differences, all of them are discussed.
Similarities
- Both contain distinct elements only
- Traversing
- Lookup
- Both can contain Hashable elements only
- Intersection, Union, and Difference
Differences
- Creation
- A Frozen set is hashable and mutable while a Set is not hashable and immutable
- A Frozen set can be used as a key in a dictionary
Creation
To create a set or a frozen set, all we need is iterable. It will only store the distinct elements.
Treversing a Set/Frozen Set
Both support ** for......in** and can be traversed.
Lookup
Both sets and frozen sets can only store hashable elements. You can not create a set of lists since a list is not hashable. Since sets and frozen sets only contain hashable elements, each element has a hash value associated with it. As a result, using the in operator takes O(1) time. Since they are unordered, both of them do not support indexing
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Intersection, Union and Difference in Sets/Frozen Sets
- Intersection : & (and)
- Union : | (pipe)
- Difference: - (subtraction)
Mutability
A set is mutable while a frozen set is not. This basically means that a set can be updated after it's created but a frozen set can not. Once a frozen set is created, the elements inside it are frozen.
Hashability
A frozen set is hashable, i.e it can have a hash value. On the other hand, a set is not hashable. As a result of this, a frozen set can be used as a key for a dictionary but a set can not be used.
Summary
- Both Frozen Sets and Sets have O(1) lookup time
- Neither of them supports indexing
- Both can be traversed using for.....in
- A set can be updated after creation but a frozen set can not be updated
- Only Frozen Sets are hashable and can be used as dictionary keys
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