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

[Terry Reedy]

On 10/7/2011 3:18 PM, Jim Jewett wrote:
> 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.

There is nothing specific to finding the index of a substring in a 
string in the above statement. If one has a collection of strings, some 
of which represent ints and some not, the failure of int(item) on some 
of them is not unexpected.

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

Please define 'inline catch' and show how to do it with str.find 
'inline' without calling the function twice.

> (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.

Again, nothing specific to why finding a substring index should be 
rather unique in having near-duplicate functions, one of which is 
clearly badly designed by using an inappropriate unix/c-ism.

-- 
Terry Jan Reedy