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Chapter 7. Dictionaries > Introduction to Dictionaries

7.1. Introduction to Dictionaries

The last standard type to add to our repertoire is the dictionary, the sole mapping type in Python. A dictionary is mutable and is another container type that can store any number of Python objects, including other container types. What makes dictionaries different from sequence type containers like lists and tuples is the way the data is stored and accessed.

Sequence types use numeric keys only (numbered sequentially as indexed offsets from the beginning of the sequence). Mapping types may use most other object types as keys, strings being the most common. Unlike sequence type keys, mapping keys are often, if not directly, associated with the data value that is stored. But because we are no longer using “sequentially-ordered” keys with mapping types, we are left with an unordered collection of data. As it turns out, this does not hinder our use because mapping types do not require a numeric value to index into a container to obtain the desired item. With a key, you are “mapped” directly to your value, hence the term “mapping type.” The most common data structure that maps keys with associated values are hash tables.


  

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