Exceptions and modules

[sam]

Hello,

consider the following code:

<module1>
import sys
import threading

class MyException(Exc eption):
pass

#from module1 import MyException

class runner(threadin g.Thread):
def __init__(self, callableObj):
self.callableOb ject=callableOb j
threading.Threa d.__init__(self )
def run(self):
try:
self.callableOb ject.makeCall()
except MyException, err:
print "MyExceptio n"
print sys.exc_type, err
except Exception, err:
print "Exception"
print sys.exc_type, err

if __name__ == '__main__':
if len(sys.argv) != 3:
print "Usage <module> <class>"
else:
callableObj = getattr(__impor t__(sys.argv[1]), sys.argv[2])()
thread=runner(c allableObj)
thread.start()
</module1>
<module2>
from module1 import MyException

class Callable:
def makeCall(self):
raise MyException("My Exception")
</module2>

Now I start the process:

python module1.py module2 Callable

And the result is:

Exception
module1.MyExcep tion MyException

So the Exception isn't recognised even though it has the same
namespace and name as the exception defined in the module. I have to
uncomment the 7th line to get my example to behave as I would like it
to.

Is this a bug/feature? Is there any reason why it shouldn't work the
way I expect it to?

Regards,

Sam Owen

[Duncan Booth]

Re: Exceptions and modules

westernsam@hotm ail.com (sam) wrote in
news:292c8da4.0 307040627.59acd a19@posting.goo gle.com:
[color=blue]
> So the Exception isn't recognised even though it has the same
> namespace and name as the exception defined in the module. I have to
> uncomment the 7th line to get my example to behave as I would like it
> to.
>
> Is this a bug/feature? Is there any reason why it shouldn't work the
> way I expect it to?[/color]

It's a feature, and it probably ought to be in the FAQ in some form.

When you run 'python module1.py' the code in the source file module1.py is
compiled into a module called __main__. That means that the line:

except MyException, err:

is actually short for:

except __main__.MyExce ption, err:

When module2 imports module1 the code is recompiled into a new module. Same
source code, but otherwise no relation. You then raise module1.MyExcep tion
which doesn't match __main__.MyExce ption.

--
Duncan Booth duncan@rcp.co.u k
int month(char *p){return(1248 64/((p[0]+p[1]-p[2]&0x1f)+1)%12 )["\5\x8\3"
"\6\7\xb\1\x9\x a\2\0\4"];} // Who said my code was obscure?