Context Manager getting str instead of AttributeError instance

Prasad, Ramit ramit.prasad at jpmorgan.com
Thu Mar 15 20:10:59 CET 2012


> Prasad, Ramit wrote:
> 
> > So I have a context manager used to catch errors
> >
> > def __exit__( self, exceptionClass, exception, tracebackObject ):
> >     if isinstance( exception, self.exceptionClasses ):
> >          #do something here
> >
> > Normally exception would be the exception instance, but for
> > AttributeError it seems to be a string instead.
> 
> I don't think so:
> 
> >>> class A(object):
> ...     def __enter__(self): return self
> ...     def __exit__(self, *args): print args
> ...
> >>> with A() as a:
> ...     a.x
> ...
> (<type 'exceptions.AttributeError'>, AttributeError("'A' object has no
> attribute 'x'",), <traceback object at 0x7f57b70f22d8>)
> Traceback (most recent call last):
>   File "<stdin>", line 2, in <module>
> AttributeError: 'A' object has no attribute 'x'
> 
> > 1) Why is AttributeError different than the other built-ins
> > in this respect?
> > 2) Are there other standard errors like this (I know
> > that SystemExit is different as well)?
> > 3) Taking into account that I want to include subclasses of
> > classes listed in self.exceptionClasses, Is there a better check I can
> > use?

Not sure why mine behaves differently:
Python 2.6.6 (r266:84292, Dec 17 2010, 12:36:53) [MSC v.1500 32 bit (Intel)] on win32
>>> 
>>> class A(object):
...     def __enter__(self): return self
...     def __exit__(self, *args): print args
...     
>>> with A() as a:
...     a.x
...     
(<type 'exceptions.AttributeError'>, "'A' object has no attribute 'x'", <traceback object at 0x1817F648>)
AttributeError: 'A' object has no attribute 'x'

As you can see, I am getting a string while you are not. 

Ramit


Ramit Prasad | JPMorgan Chase Investment Bank | Currencies Technology
712 Main Street | Houston, TX 77002
work phone: 713 - 216 - 5423

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