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iter(callable, sentinel) runs callable synchronously, so one that calls an external/OS function cannot suspend and
raises NotImplementedError. Same limitation as map/filter/sorted(key=...).iter(callable, sentinel) compares result == sentinel, where CPython compares sentinel == result; only observable
if the two sides have asymmetric __eq__.- A
StopIteration raised by callable propagates; CPython treats it as clean exhaustion and stops iterating.
- A user instance defining
__call__ is rejected as not callable, since __call__ is not dispatched (see
classes.md).
- The vendored type stub is upstream typeshed’s verbatim, so
-t accepts iter(obj) for an object with only
__getitem__; Monty has no __getitem__ iteration fallback and raises TypeError at runtime.
-t accepts for x in obj (though not a, b = obj) for a class that opts out of iteration with __iter__ = None,
which raises TypeError at runtime as it does in CPython.- Built-in iterators do not expose their dunders as attributes:
hasattr(iter([1]), '__iter__') is False, where
CPython reports True. Iteration itself works; only attribute lookup of the dunder differs. This covers every
built-in iterator, including the itertools adaptors.
- Iterator-specific attributes such as
__length_hint__ are not exposed.