[Python-ideas] Generators are iterators

Stephen J. Turnbull stephen at xemacs.org
Tue Dec 16 06:48:23 CET 2014

Juancarlo Añez writes:

 > Most newcomers to programming take a while to grok complex control
 > flows, and what's happening here is too complex even for Python
 > contributors.

As I understand Raymond's point, what is happening here is *not*
particularly complex (I don't see it as complex myself, anyway).  It's
simply an obscure (because rare) and obvious (once you know about it)
consequence of two simple design decisions: "exceptions bubble" and
"iterator termination is signaled with an exception".  That obscurity
is compounded by the fact that a programmer error will pass silently.
(There must be a theorem that says that in any Turing complete
language some errors will pass silently!)

In the case of *generators* silently ignoring an error is unnecessary,
and PEP 479 fixes that one case, at a cost of breaking a useful idiom
in some functions.

For iterators in general, I suppose we could add a flag to checkers to
look for function calls inside iterators, and warn the user to check
for the potential for spuriously raising StopIteration.  (I doubt
that's a great idea, but it could be done.)

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