[Zope3-dev] Please, no bare 'except:' clauses!

[Steve Alexander]

Today, I was looking through the code for various placeful services, 
with a view to writing my own placeful service.

I came across various bare 'except:' clauses in the ErrorReporting Service

Zope/App/OFS/Services/ErrorReportingService/ErrorReportingService.py

http://cvs.zope.org/~checkout~/Zope3/lib/python/Zope/App/OFS/Services/ErrorReportingService/ErrorReportingService.py?rev=1.5&content-type=text/plain

The problems with these bare 'except:' clauses are:

* They hide errors by consuming all exceptions.

* They are hard to correct and replace with specific exceptions, because
   the original author did not explain the rationale for the except
   clause.


Bare 'except:' clauses caused a number of problems with Zope2. There was 
a very time-consuming purge on them several months ago. I don't want us 
to have to do the same thing for Zope 3.

My recommendations:

* Do not use bare 'except:' clauses. Always qualify them with specific
   exception types.

* If you do need to use a bare 'except:' clause, add a comment before it
   explaining that you used this bare except clause mindfully, and
   explaining the kinds of exception you need to catch, and the reason
   the bare 'except:' clause is needed.


Tomorrow I shall check in a change that adds a '# XXX' comment above 
each bare 'except:' clause I found. I'd appreciate it if someone who 
understands how the code is meant to work can either check in a change 
with specific exceptions, or contact me to give me pointers on how to 
make the exceptions more specific.


Thanks.

--
Steve Alexander