[Python-ideas] Default return values to int and float

[Jim Jewett]

On Thu, Oct 6, 2011 at 6:04 PM, Terry Reedy <tjreedy at udel.edu> wrote:
> On 10/6/2011 4:32 PM, Jim Jewett wrote:
>> On Wed, Oct 5, 2011 at 5:17 PM, Terry Reedy<tjreedy at udel.edu>  wrote:
>>> On 10/4/2011 10:21 PM, Guido van Rossum wrote:

>>>> We also have str.index which raised an exception, but people dislike
>>>> writing try/except blocks.

>>> ... try/except blocks are routinely used for flow control in Python
>>> ... even advocate using them over if/else (leap first)

>> str.index is a "little" method that it is tempting to use inline, even
>> as part of a comprehension.

> That is an argument *for* raising an exception on error.

Only for something that is truly an unexpected error.  Bad or missing
data should not prevent the program from processing what it can.

When I want an inline catch, it always meets the following criteria:

(a)  The "exception" is actually expected, at least occasionally.
(b)  The exception is caused by (bad/missing/irrelevant...) input --
nothing is wrong with my computational environment.
(c)  I do NOT need extra user input; I already know what to do with it.

Typically, I just filter it out, though I may replace it with a
placeholder and/or echo it to another output stream instead.

(d)  The algorithm SHOULD continue to process the remaining (mostly good) data.


Sometimes, the "bad" data is itself in a known format (like a "."
instead of a number); but ... not always.

-jJ