exceptions with spaces don't work??

[John J Lee]

On Mon, 7 Apr 2003, Paul Probert wrote:
> As a python newbie, I came across a problem:
> If I raise an exception with a string, as in:
>     raise 'somestring'
> then my statement
>     except 'somestring':
> will catch it unless there are spaces. For instance
> suppose I have a file ext.py:
[...]

1. Don't Do That.  String exceptions are deprecated.  Use a real exception
object instead:

class SomeError(Exception): pass

2. I think your theory about spaces in strings wouldn't stand up to some
experimentation with longer strings.  IIRC, catching a string exception
requires identity of the string objects, not mere equality -- they must be
the same object.  So:

someerror = "somestring"
try:
    raise someerror
except someerror:
    assert 1

is guaranteed to work (at least until string exceptions finally get
prohibited), while:

try:
    raise "someerror"
except "someerror":
    assert 1

is not.  Maybe it happens to work sometimes because Python is caching
short strings, so the two occurrences of "someerror" happen to be the same
object in memory.


John