frozenset() Immutable set
Last updated: 2026-09-22
frozenset() Immutable set
frozenset() returns an immutable set; elements must be hashable, and frozenset itself is hashable (can be a dict key).
| Category | Built-in Functions |
|---|---|
| Kind | Built-in Function |
| Python Version | all |
📝 Syntax
frozenset([iterable])⚙️ Parameters
| iterable Optional | An iterable; omitted yields an empty frozenset.（Default：None） |
|---|
Returns：frozenset. An immutable, hashable set.
💥 Raises
TypeError— Raised when an element of iterable is unhashable.
▶ Example
Edit the code, press Run, and see the result in the output panel:
Output：
frozenset({1, 2, 3})
{frozenset({1, 2, 3}): 'value'}🏷️ Related Built-in Functions
💡 Related Cases
More case studies coming soon — check back later.
❓ FAQ
QWhat is the difference between frozenset and set?
AThe one key difference is that frozenset is immutable (no add/remove/update), and therefore hashable — it can be a dict key or placed inside another set.
QWhy is {frozenset([1,2]): 'x'} valid while {set([1,2]): 'x'} raises an error?
AA dict key must be hashable: frozenset is immutable so it is hashable, while set is mutable so it is not — raising TypeError: unhashable type: 'set'.
QDoes frozenset deduplicate?
AYes, like set, frozenset([1, 2, 2, 3]) yields frozenset({1, 2, 3}).
QCan frozenset be converted back to set?
AYes, set(fs) returns a mutable copy with the same elements; conversely, a set can also be converted to frozenset.
