in place list modification necessary? What's a better idiom?

[MRAB]

andrew cooke wrote:
> R. David Murray wrote:
>>>   [...]
>>>   try:
>>>     dimensions.append(float(s))
>>>   except:
>>>     dimensions.append(float(quantization[s]))
>> No, no, no; never use a bare except! :)
> 
> can you explain why?  i can't think of any reason why the code would be
> better catching a specific exception.
> 
> as a general rule, maybe, but in this particular case i can't see a reason
> - so i'm not sure if you're just pedantically following rules or if i've
> missed something i should know.
> 
A bare exception will catch _any_ exception, even those you didn't
expect (technical term: "bug" :-)); for example, if you had written:

     try:
         dimension.append(float(s))
     except:
         dimensions.append(float(quantization[s]))

it would silently catch "NameError: name 'dimension' is not defined" and
perform the fallback action.