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Named tuples

Named tuples can be constructed with collections.namedtuple (see collections.md), and also enter the sandbox as sys.version_info, as the time module’s struct_time (see time.md) and as values passed in from the host via the MontyObject API. typing.NamedTuple is a marker only; subscripting it or inheriting from it does not produce a type, since there is no class inheritance (see classes.md).

Instances behave as CPython named tuples: integer indexing, attribute access, len/iteration/bool, equality and hashing against equivalent plain tuples, and the inherited tuple surface (membership, count, index, ordering against plain tuples and other namedtuple classes alike, slicing, concatenation, and repetition, each producing a plain tuple). _fields, _field_defaults, _make, _replace and _asdict require a collections.namedtuple class: sys.version_info, time.gmtime() and host-supplied named tuples model CPython structseqs, which expose none of them (sys.version_info._fields raises AttributeError, as in CPython).

Divergences

  • Concatenating with a list reports TypeError: unsupported operand type(s) for +: 'namedtuple' and 'list' where CPython says can only concatenate tuple (not "list") to tuple. Monty’s plain tuples word it the same way, so this is not namedtuple-specific.
  • Accessing a method without calling it (m = p._asdict) raises AttributeError: methods are call-only, not bound-method values. Repo-wide, [1].append, 'a'.upper and {}.get all do the same.
  • Subclassing is unsupported (see classes.md).
  • Subscripting the class (Point[int]) raises TypeError: type 'Point' is not subscriptable; CPython builds a types.GenericAlias through the inherited tuple.__class_getitem__ (see typing.md).