Why does {1} == frozenset({1}) in Python?

Question

I find it odd that in Python, {1} == frozenset({1}) evaluates to True. set and frozenset are different object types, and I don't see this similarity between other iterable object types (ex. {1} == (1,) evaluates to False). Why does this behavior occur with sets? Are there other iterable object types that have similar behavior?

Answer 1

As per the documentation python2 and documentation python3

Instances of set are compared to instances of frozenset based on their members. For example, "set('abc') == frozenset('abc')" returns True.

and in the python3 documentation:

Both set and frozenset support set to set comparisons. Two sets are equal if and only if every element of each set is contained in the other (each is a subset of the other). A set is less than another set if and only if the first set is a proper subset of the second set (is a subset, but is not equal). A set is greater than another set if and only if the first set is a proper superset of the second set (is a superset, but is not equal).