How to catch str exception?

[anuraguniyal]

import sys
try:
raise "xxx"
except str,e:
print "1",e # is not caught here
except:# is caught here
print "2",sys.exc_type,sys.exc_value

In the above code a string exception is raised which though deprecated
but still a 3rd party library I use uses it. So how can I catch such
exception without relying on catch all, which could be bad.

system: Python 2.5.2 (r252:60911, Jul 31 2008, 17:28:52) [GCC 4.2.3
(Ubuntu 4.2.3-2ubuntu7)] on linux2

 

[Kurt Symanzik]

import sys
try:
raise "xxx"
except str,e:
print "1",e # is not caught here
except:# is caught here
print "2",sys.exc_type,sys.exc_value

In the above code a string exception is raised which though deprecated
but still a 3rd party library I use uses it. So how can I catch such
exception without relying on catch all, which could be bad.

system: Python 2.5.2 (r252:60911, Jul 31 2008, 17:28:52) [GCC 4.2.3
(Ubuntu 4.2.3-2ubuntu7)] on linux2

Try this, i.e. catch the exact string:

except "xxx":


Kurt

 

[anuraguniyal]

but the whole point of catching such exception is that i can print its
value
there are many such exceptions and hence it is not feasible to catch
them all or know them all unless i go thru src code.

 

[Peter Otten]

but the whole point of catching such exception is that i can print its
value
there are many such exceptions and hence it is not feasible to catch
them all or know them all unless i go thru src code.

Catch them all with a bare except and then reraise non-string exceptions:

try:
raise "abc"
except:
e, t, tb = sys.exc_info()
if not isinstance(e, str):
raise
print "caught", e

 

[anuraguniyal]

try:
    raise "abc"
except:
    e, t, tb = sys.exc_info()
    if not isinstance(e, str):
        raise
    print "caught", e

This seems to be the solution, thanks

 

[Dave Angel]

import sys
try:
raise "xxx"
except str,e:
print "1",e # is not caught here
except:# is caught here
print "2",sys.exc_type,sys.exc_value

In the above code a string exception is raised which though deprecated
but still a 3rd party library I use uses it. So how can I catch such
exception without relying on catch all, which could be bad.

system: Python 2.5.2 (r252:60911, Jul 31 2008, 17:28:52) [GCC 4.2.3
(Ubuntu 4.2.3-2ubuntu7)] on linux2

Just fix the except type to be the exception caused by the illegal "raise"

except TypeError,e:
print "1",e # is caught here


1 exceptions must be classes or instances, not str

 

[anuraguniyal]

except TypeError,e:
    print "1",e # is caught here

1 exceptions must be classes or instances, not str

doesn't happen so in 2.5.2

 

[MRAB]

but the whole point of catching such exception is that i can print its
value
there are many such exceptions and hence it is not feasible to catch
them all or know them all unless i go thru src code.

If string exceptions are so difficult to use, don't use them!

It would be better to write your own exception class:

class MyException(Exception):
pass

try:
raise MyException("Something bad happened!")
except MyException, e:
print "ERROR: %s" % e

 

[anuraguniyal]

It would be better to write your own exception class:

class MyException(Exception):
     pass

and how would i automatically inject this into 3rd part library

 

[MRAB]

and how would i automatically inject this into 3rd part library

Ah, I wasn't reading carefully enough!

 

[Dave Angel]

doesn't happen so in 2.5.2

I tested it in 2.6.2

Perhaps you could try something like:

try:
raise "xxx"
except Exception, e:
print "1",e # is caught here
...and then test e.message and reraise if necessary

 

[Terry Reedy]

but the whole point of catching such exception is that i can print its
value
there are many such exceptions and hence it is not feasible to catch
them all or know them all unless i go thru src code.

I think you have discovered why they are gone in Py3 ;-).

 

[Paul Rubin]

there are many such exceptions and hence it is not feasible to catch
them all or know them all unless i go thru src code.

But that is true of all exceptions. The alternative seems to be a
"checked exception" scheme like Java's, which in practice imposes a
huge pain on programmers, who have to modify type signatures all up
and down the call hierarchy every time they raise another exception at
the bottom level.

 

[MRAB]

But that is true of all exceptions. The alternative seems to be a
"checked exception" scheme like Java's, which in practice imposes a
huge pain on programmers, who have to modify type signatures all up
and down the call hierarchy every time they raise another exception at
the bottom level.

I would've thought that a modern IDE would do a lot of the work for you.

 

[Rhodri James]

This seems to be the solution, thanks

Do be aware that string exceptions are going away, so at
some point you're going to upgrade your version of Python
and your scripts will mysteriously stop working. Peter's
patch will help you for now, but it's a double-edged sword
in that it also lets you pretend that you don't have to
fix the problem properly later. In my experience it's
generally best to fix the problem now rather than paper
over the cracks.

Since this is a third-party library doing this, as far as
I can see it you have three choices:

1) Get hold of a more up-to-date version of the module,
if there is one.

2) Ask the module writers nicely to fix the problem.

3) Fix it yourself.

The beauty of Python is that 3) isn't all that hard!