Can you explain what data types can be hashed?

In Python, "hashable" data types refer to objects that have an immutable state and support the __hash__() method. This means their value does not change after creation, and they can be used as keys in dictionaries or elements of sets.

Typical hashable types include:

• Numbers (int, float, complex)
• Strings (str)
• Tuples (tuple), if all elements inside are also hashable
• Boolean values (bool)

Unhashable types are mutable objects, such as lists (list), dictionaries (dict), sets (set), because their contents can change, which would break hash integrity.

Example:

hash(42)          # works
hash("hello")    # works
hash((1, 2, 3))   # works
hash([1, 2, 3])   # TypeError: unhashable type: 'list'