[capi-sig] String to number conversion

[M.-A. Lemburg]

On 2008-05-07 18:50, Rasmus Andersson wrote:
> 
> On 7 maj 2008, at 18.40, 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)

Didn't I just give you a few ?

> 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.

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