Are python collections mutable?

A set is an unordered, mutable sequence. The elements in the collection must be hashable, that is, immutable data types.

Empty collection

a=set()

Note that a={} creates an empty dictionary.

set - a mutable set. Elements in the collection can be added or deleted dynamically.

frozenset - Immutable collection. The elements in the collection are immutable.

Note: The return value of union, intersection, difference, etc. has the same type as the leftmost operand. For example: s & t take the intersection. If the s collection is a set type collection and the t collection is a frozenset type collection, the returned result will be a set type collection.

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You can also use set() to convert it into a set

b=[1,2,3,4]
a=set(b)
a
{1,2,3,4}

You can also use {} to create one Set

a={1,2,3,4,1}
a
{1,2,3,4}

is the same as a dictionary, because the set is unordered, so when there are duplicate elements, only one of them is retained.

An immutable set is an unordered immutable set

Use frozenset(seq) to create

a=frozenset([1,2,3,(1,2,4)])
a
frozenset({1,2,3,(1,2,4)})

Elements can only be hashable The

frozenset([1,2,3,[1,2,4]])
error

is mainly used as a dictionary key. . The difference from tuple is that it is unordered, the elements are not repeatable, and the elements can only be of immutable type.

Description: You can convert other combined data types into immutable collection types (or convert mutable collection type set into immutable collection type frozenset), and return an immutable collection type with no duplicate elements and arbitrary ordering. variable set.

frozenset() function

Syntax: frozenset() -> empty frozenset object Returns an immutable empty set

frozenset(iterable) - > frozenset object Returns an immutable new set

iterable - the combined data type to be converted.

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