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Does Python Offer a Native Ordered Set, and How Can One Be Emulated?

Barbara Streisand

Jan 05, 2025 am 11:04 AM

Does Python Offer a Native Ordered Set, and How Can One Be Emulated?

Exploring Ordered Sets in Python

Python offers an ordered dictionary, but does it provide an ordered set? Let's delve into this query and uncover the potential solutions available in Python.

The Absence of Ordered Sets

Unlike ordered dictionaries, Python does not natively support ordered sets. However, introducing ordered sets can be a beneficial feature for maintaining the order of elements while eliminating duplicates.

Emulating Ordered Sets with Dictionaries

Starting with Python 3.7, a simple dictionary can be utilized as an ordered set by employing the dict class method fromkeys(). This method takes only keys (setting values to None), effectively emulating ordered set functionality.

Example Usage

To showcase the usage, consider a list of keywords: ['foo', 'bar', 'bar', 'foo', 'baz', 'foo']. To filter out duplicates while preserving order, simply use the fromkeys() method and retrieve the keys().

>>> keywords = ['foo', 'bar', 'bar', 'foo', 'baz', 'foo']

>>> list(dict.fromkeys(keywords))
['foo', 'bar', 'baz']

Alternative for Older Python Versions

For older Python versions, the collections.OrderedDict class can serve as an ordered set. It provides similar functionality to emulating ordered sets with dictionaries.

In conclusion, while Python does not offer native ordered sets, clever use of dictionaries and the collections.OrderedDict class can effectively accomplish the same task, enabling developers to handle ordered sets in their Python code.

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