try: except <never>:

[Hallvard B Furuseth]

I'd like an 'except <exception which is never raised>' statement
Is there a defined way to do that, for Python 2.2 and above?
'except None:' works for now, but I don't know if that's safe:

for ex in ZeroDivisionError, None:
try:
1/0
except ex:
print "Ignored first exception."

I could just use
except ZeroDivisionError:
if not <first iteration>:
raise
print "Ignored first exception."
but the variant above gets a bit neater.

--
Hallvard

[Paul Rubin]

Hallvard B Furuseth <h.**********@usit.uio.no> writes:

'except None:' works for now, but I don't know if that's safe:

for ex in ZeroDivisionError, None:
try:
1/0
except ex:
print "Ignored first exception."

class NeverRaised(Exception): pass

for ex in ZeroDivisionError, NeverRaised:
...

[Hallvard B Furuseth]

Paul Rubin writes:

Hallvard B Furuseth <h.**********@usit.uio.no> writes:

'except None:' works for now, but I don't know if that's safe:

for ex in ZeroDivisionError, None:
try:
1/0
except ex:
print "Ignored first exception."

class NeverRaised(Exception): pass

for ex in ZeroDivisionError, NeverRaised:

Heh. Simple enough. Unless some obstinate person raises it anyway...

--
Hallvard

[Paul Rubin]

Hallvard B Furuseth <h.**********@usit.uio.no> writes:

class NeverRaised(Exception): pass
for ex in ZeroDivisionError, NeverRaised:

Heh. Simple enough. Unless some obstinate person raises it anyway...

Hmm, ok, how's this?:

def NeverRaised():
class blorp(Exception): pass
return blorp
for ex in ZeroDivisionError, NeverRaised():
...

[Duncan Booth]

Paul Rubin wrote:

Hallvard B Furuseth <h.**********@usit.uio.no> writes:

> class NeverRaised(Exception): pass
> for ex in ZeroDivisionError, NeverRaised:

Heh. Simple enough. Unless some obstinate person raises it anyway...

Hmm, ok, how's this?:

def NeverRaised():
class blorp(Exception): pass
return blorp
for ex in ZeroDivisionError, NeverRaised():
...

Or you can create an unraisable exception:

\ class NeverRaised(Exception):
def __init__(self, *args):
raise RuntimeError('NeverRaised should never be raised')
\

try:
raise NeverRaised
except NeverRaised:
print "caught it"

Traceback (most recent call last):
File "<pyshell#47>", line 4, in __init__
raise RuntimeError('NeverRaised should never be raised')
RuntimeError: NeverRaised should never be raised

[Tom Anderson]

On Tue, 10 Jan 2006, Duncan Booth wrote:

Paul Rubin wrote:

Hallvard B Furuseth <h.**********@usit.uio.no> writes:

class NeverRaised(Exception): pass
for ex in ZeroDivisionError, NeverRaised:

Heh. Simple enough. Unless some obstinate person raises it anyway...
Hmm, ok, how's this?:

def NeverRaised():
class blorp(Exception): pass
return blorp
for ex in ZeroDivisionError, NeverRaised():
...
Nice.
Or you can create an unraisable exception:
\

class NeverRaised(Exception):
def __init__(self, *args):
raise RuntimeError('NeverRaised should never be raised')

Briliant! Although i'd be tempted to define an UnraisableExceptionError to
signal what's happened. Or ...

class ImpossibleException(Exception):
def __init__(self, *args):
raise ImpossibleException, args

Although crashing the interpreter is probably overkill.

tom

--
Like Kurosawa i make mad films; okay, i don't make films, but if i did
they'd have a samurai.

[Duncan Booth]

Tom Anderson wrote:

class NeverRaised(Exception):
def __init__(self, *args):
raise RuntimeError('NeverRaised should never be raised')

Briliant! Although i'd be tempted to define an
UnraisableExceptionError to signal what's happened. Or ...

class ImpossibleException(Exception):
def __init__(self, *args):
raise ImpossibleException, args

Although crashing the interpreter is probably overkill.

Crashng the interpreter would be, but what you just wrote is simply a more
obscure way of raising RuntimeError :-)

class ImpossibleException(Exception): .... def __init__(self, *args):
.... raise ImpossibleException, args
.... raise ImpossibleException

Traceback (most recent call last):
File "<stdin>", line 3, in __init__
RuntimeError: maximum recursion depth exceeded

[Hallvard B Furuseth]

Thanks for the help.

Tom Anderson writes:

class NeverRaised(Exception):
def __init__(self, *args):
raise RuntimeError('NeverRaised should never be raised')

Briliant! Although i'd be tempted to define an UnraisableExceptionError
to signal what's happened. Or ...

A package we are using has ProgrammingError (like AssertionError except
__debug__ doesn't disable it), and RealityError when something *really*
can't happen:-)

--
Hallvard