What Makes a Python Object Hashable?

Understanding the Concept of "Hashable" in Python

In Python programming, "hashable" refers to objects that possess specific characteristics, enabling them to be used as dictionary keys or set members.

Definition of Hashability

According to the Python glossary, an object is hashable if it meets the following criteria:

• It has an immutable hash value that remains constant throughout its lifetime. This is achieved through the __hash__() method.
• It can be compared to other objects for equality (using the __eq__() or __cmp__() methods). Hashable objects that are equal must have the same hash value.

Significance of Hashability

Hashability plays a crucial role in data structures such as dictionaries and sets. These structures use hash values internally to efficiently locate and access elements. By being hashable, objects can be used as keys in dictionaries or members in sets, allowing for faster lookups and membership checks.

Immutability and Hashability

All immutable built-in objects in Python, such as numbers, strings, and tuples, are inherently hashable. On the other hand, mutable containers like lists and dictionaries are not hashable, as their contents can change.

User-Defined Class Objects

Objects instantiated from user-defined classes are hashable by default. Each object has a unique hash value equal to its id(). However, it's possible to override the __hash__() method in custom classes to define a custom hash function.

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