As yet, I don't have a particularly firm opinion on whether or not block
statements should support an 'else:' clause. And there are obviously a great
many other questions to be answered about how block statements might work that
are more important than this one.
Still, I've been tinkering with some ideas for how to approach this, and thought
I'd write them up for everyone else's consideration.
Option 0:
No else clause allowed. Figured I should mention this, since it is Guido's
last reported inclination, and my total lack of use cases for the other options
below suggests this is the best idea for an initial implementation.
Option 1: mimic try, for, while semantics
An 'else' clause on a block statement behaves like the else clause on for
and while loops, and on try/except statements - the clause is executed only if
the managed suite completes 'normally' (i.e. it is not terminated early due to
an exception, a break statement or a return statement)
Option 2: mimic if semantics
An 'else' clause on a block statement behaves vaguely like the else clause on
an if statement - the clause is executed only if the first suite is never
entered, but no exception occurs (i.e. StopIteration is raised by the first call
to next).
Option 3: iterator-controlled semantics
The iterator is given the ability to control whether or not the else clause
is executed (e.g. via an attribute of StopIteration), probably using option 1
above as the default behaviour.
Cheers,
Nick.
--
Nick Coghlan | ncoghlan at gmail.com | Brisbane, Australia
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