How deeply does Python Workout: 50 ten-minute exercises cover hashable?

Defines hashability through hash(), contrasts O(n) sequence search with O(1) dictionary lookup, and only raises collision handling.

Hashable

As explained in Python Workout: 50 ten-minute exercises

A hashable type has values with stable hash values and can therefore be used for dictionary keys or set elements.

A hashable type supports the hash function, so its values can serve as dictionary keys. Hashing helps keep keys unique and makes lookup fast rather than requiring a sequential search. section 4.1

Why hashing speeds lookup

Searching a string, list, or tuple may examine values one by one, taking O(n) time. A dictionary uses a hash-based location, analogous to sending visitors directly to an office by the first letter of a surname, giving approximately O(1) lookup. section 4.1

Keep these dictionary rules in mind:

Keys must be hashable, such as numbers or strings. section 4.23
Values can contain anything, including another dictionary. section 4.23
Keys are unique, and they can be iterated with loops or comprehensions. section 4.23

How Python Workout: 50 ten-minute exercises covers it

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Python How-ToA hashable object is a Python object with a stable hash value and equality behavior that allow it to serve as a dictionary key or set element.
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Python Workout, Second EditionA hashable object is a Python object with a stable hash value that can be used as a dictionary key.

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Related concepts

Mapused by · A map is an associative data structure that stores key-value pairs and supports retrieving values by key.
unhashablecontrasts with · In Python, unhashable describes an object that cannot be used as a dictionary key or set element because it lacks a suitable stable hash value.
statecontrasts with · State is information or a configuration describing the condition of a system, entity, or computation at a particular time and potentially influencing subsequent behavior or decisions.
immutable collectionequivalent to · An immutable collection is a collection whose membership and contents cannot be changed after creation.
similarity searchproduces · Similarity search is a retrieval technique that finds or ranks items by comparing their representations with a query according to a similarity or distance measure.

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