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Python Essentials by Steven F. Lott

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Mappings

Python has a number of mapping collections. A mapping is an association between a key and a value. The built-in mapping collection is the dict class. The other mappings are defined in the collections library, and must be imported.

Items that are keys within a mapping must be immutable; they must provide a proper hash value as well as a matching equality test. The values within a mapping have no restrictions; they can be mutable or immutable. The order of the keys is not maintained by the dict class.

We can create a simple dict display using {}; each key and value are separated by the : character.

Here's an example of a simple mapping:

sieve = {2: True, 3: True, 4: False, 5: True, 6: None, 7: None}

We've created a simple mapping with keys ...

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