Documentation

frozendict was added as a built-in type in 3.15 (PEP 814) and is documented in
the data model ("Frozen dictionaries" in Doc/reference/datamodel.rst), but
Doc/reference/expressions.rst still lists only dict wherever it enumerates
built-in mapping types. Three places seem to need an update:

1. "Value comparisons", the bullet about mappings:

   Mappings (instances of :class:dict) compare equal if and only if they have
   equal (key, value) pairs. [...]

   frozendict is not a subclass of dict, so it is not covered by "instances of
   dict", yet it follows the same rules, and the two types compare equal to each
   other:

   dict(a=1, b=2) == frozendict(a=1, b=2)
   True

   Suggested: "Mappings (instances of :class:dict or :class:frozendict)
   compare equal if and only if they have equal (key, value) pairs."
   The following sentence about order comparisons raising TypeError applies to
   frozendict as well.

2. "Membership test operations":

   For container types such as list, tuple, set, frozenset, dict, or
   collections.deque, the expression x in y is equivalent to
   any(x is e or x == e for e in y).

   Suggested: add frozendict to the list.

3. "Boolean operations", the list of values interpreted as false:

   [...] and empty strings and containers (including strings, tuples, lists,
   dictionaries, sets and frozensets).

   Suggested: add "frozendicts" (an empty frozendict is false like any other
   empty container).

Minor, optional: the section "Binary arithmetic operations" says that some of
these operations apply to non-numeric types, but only describes numbers and
sequences. The - operator on sets (difference) and | on dicts are not
mentioned there (they are documented with the types themselves).

Linked PRs

• gh-161608: Mention frozendict in the expressions reference #161612