[capi-sig] String to number conversion

[Rasmus Andersson]

On 7 maj 2008, at 18.40, M.-A. Lemburg wrote:

> On 2008-05-07 18:28, Rasmus Andersson wrote:
>> On 7 maj 2008, at 17.46, M.-A. Lemburg wrote:
>>> On 2008-05-07 17:27, Hrvoje Niksic wrote:
>>>> I miss a function able to convert the string representation of a
>>>> Python primitive number (int, long, float, complex) to an actual
>>>> number, basically the reverse of repr for numbers.
>>>> <snip>
>>>> Would anyone else find this kind of function useful?
>>>
>>> Yes.
>>>
>>> Perhaps as PyNumber_FromString() ?!
>> I rarely wrap primitives in objects, as this increases both memory  
>> usage, complexity and overhead.  (However, sometimes you _might_  
>> need to, but I can't come up with a scenario)
>> So, in most cases this would probably happen:
>> PyObject *num = PyNumber_FromString(num_s);
>> if(!PyLong_Check(num)) {
>>  // Error...
>> }
>> else {
>>  self->event_id = PyLong_AsLongLong(num);
>> }
>
> Not really. The point of the PyNumber_* API is to work on numbers
> without actually caring or knowing the specific number types
> (Include/abstract.h).

Yes I know, but I can't really see a big need for this kind of  
functionality in practice, but please, enlighten me! (maybe with a  
scenario)

By the way, great to see something happing on this list. Has been  
awfully quiet! :)

>
> You'd only do the final conversion to a specific number type
> at the very end of the calculation using e.g. PyNumber_Int().
>
> In some cases, not even that, since all you're interested in
> is converting some object to a number object and then passing
> that to e.g. marshal.
>
>> And you lose, because this would be simpler:
>> self->event_id = strtoll(PyString_AsString(num_s), (char *)NULL, 10);
>> if(errno == EINVAL) {
>>  // Error...
>> }
>> Meaning, you rarely need to take input which can be any kind of  
>> number manifested as a string and return it as any number  
>> manifested as a native number. (The examples above indicate the  
>> output type is known (signed 64bit integer))
>> Could you maybe give a real-world scenario where this would be  
>> needed? Where neither the input not the output number type is known.
>
> Parsing numeric data and converting it to some other format.
>
> -- 
> Marc-Andre Lemburg
> eGenix.com
>
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> 2008)
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Rasmus Andersson
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