How Does Python Maintain Order in Dictionaries?

Maintaining Order in Python Dictionaries

Determining the order of keys and values in a Python dictionary can be a challenge if the order is not inherently related to the values themselves. However, from Python 3.6 onwards, the standard dict type now maintains insertion order by default.

To preserve the order in which you declare keys and values, simply define your dictionary as follows:

d = {'ac': 33, 'gw': 20, 'ap': 102, 'za': 321, 'bs': 10}

This will ensure that the dictionary keys are stored in the order they were listed in the source code.

This feature was introduced by using an array with integers for the sparse hash table, where those integers index into an array that stores the key-value pairs. This array inherently stores items in insertion order, resulting in improved memory usage compared to previous Python versions.

In Python 3.7, the order-preserving aspect of the dict type became a language specification, making it mandatory for all Python implementations compatible with that version or newer to preserve order in dictionaries.

While dict types now maintain insertion order by default, you may still consider using the collections.OrderedDict() class in certain cases. It offers additional functionality, including reversibility and support for reordering items using the move_to_end() method.

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