[capi-sig] String to number conversion

[M.-A. Lemburg]

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).

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
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