In Soni's original code snippet, there is a clear separation of code
that is inside the try block from code that is outside the try block:
> def a_potentially_recursive_function(some, args):
> try:
> some.user_code()
> except ExceptionWeCareAbout as exc:
> raise RuntimeError from exc
> code_we_assume_is_safe() # and more code following...
This is good exception hygiene.
Only some.user_code is guarded by the try block. If it turns out that
code_we_assume_is_safe is not actually safe, and fails with an
exception, it won't be caught by the try block and you will know about
it.
In your re-written syntactic sugar, you have:
# new syntax
> def a_potentially_recursive_function(some, args) with ExceptionWeCareAbout:
> some.user_code()
> code_we_assume_is_safe() # and more code following...
which becomes:
> def a_potentially_recursive_function(some, args):
> try:
> some.user_code()
> code_we_assume_is_safe() # and more code following...
> except ExceptionWeCareAbout as exc:
which is the opposite of good exception hygiene. Too much code,
including the wrong code, is guarded by the try block, which means that
the compiler has to *guess your meaning* and set a flag to decide
whether to re-raise the exception or run the except block.
Its not clear how the compiler guesses that. Is it only because you have
an explicit `raise ExceptionWeCareAbout` in the code? What if the
exception is not explicit?
# explicitly raising ExceptionWeCareAbout
raise ExceptionWeCareAbout
# not explicit
raise some_exception_object_we_prepared_earlier
raise prepare_exception(*args) # returns an ExceptionWeCareAbout instance
verify_or_raise(condition) # raises ExceptionWeCareAbout
> Obviously this doesn't solve exception handling, doesn't require the
> caller to catch the exceptions, etc etc.
So that's two points against it.
> It does, however, encourage better exception hygiene.
Except it doesn't, it makes it worse. So that's three points against it.
> Chances are something like this would
> significantly reduce the amount of swallowed exceptions, if it gets
> widely adopted.
Or based on your examples, increase the number of swallowed exceptions,
and be much harder to refactor code safely.
--
Steve
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