[Python-ideas] except expression

[Chris Angelico]

On Wed, Feb 19, 2014 at 2:13 AM, MRAB <python at mrabarnett.plus.com> wrote:
> Another possibility would be to say that a bare except in an expression
> catches only certain "expression-oriented" exceptions, e.g. ValueError.
> The simplest way to do that would be to make them subclasses of an
> ExpressionError class. The question then becomes one of which
> exceptions are "expression-oriented"...

Easier than fiddling with class inheritance would be to make
ExpressionError into a tuple of exception types - at least for testing
purposes. If this _is_ to be done, I would definitely advocate having
that name (or some equivalent) as a built-in, so it's straight-forward
to either manipulate it or use it in a statement-except. But you're
absolutely right that the question of which ones are
expression-oriented would be a big one. I could imagine catching
(ValueError, Unicode{En,De}codeError, AttributeError, EOFError,
IOError, OSError, LookupError, NameError, ZeroDivisionError) and
that's just from a quick skim of the built-in names. Would you
consider making a tuple like that and then using "except
CommonErrors:" all over your code? Or more to the point, if it were
really convenient to do that, would it improve your code?

ChrisA