On Wed, 24 Sep 2008 10:54:40 -0500, Grant Edwards wrote:
> You're right. I had forgotten that sys.exit() is actually raising the
> system exit exception, and that the application calling the library
> could handle that exception.
Could but shouldn't.
The exception hierarchy was re-designed in Python 2.5 specifically so
that SystemExit and KeyboardInterrupt no longer inherit from Exception.
That means this will do the right thing:
try:
process(record)
if changed:
update(record)
except Exception:
# don't write the record if any error occurs
pass
Neither SystemExit nor KeyboardInterrupt are errors, and they should not
be treated as errors. I quote from the Fine Manual:
[SystemExit] inherits from BaseException instead of StandardError or
Exception so that it is not accidentally caught by code that catches
Exception. This allows the exception to properly propagate up and cause
the interpreter to exit.
http://docs.python.org/lib/module-exceptions.html
SystemExit is not an error. KeyboardInterrupt is not an error. Libraries
should not use SystemExit to signal an error any more than they should
use MemoryError to signal a missing attribute.
Whether or not an application exits is up to the application to decide,
not the library it wraps. Libraries should report errors by raising an
Exception (note the capital E), and the application should decide whether
or not it is recoverable, and if not, exit (perhaps by simply not
catching the exception).
--
Steven
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