Re: proposal: PL/Pythonu - function ereport

2016-02-18 17:59 GMT+01:00 Catalin Iacob <iacobcatalin(at)gmail(dot)com>:

> On 2/18/16, Pavel Stehule <pavel(dot)stehule(at)gmail(dot)com> wrote:
> > it doesn't look badly. Is there any possibility how to emulate it with
> > Python2 ? What do you think about some similar implementation on Python2?
>
> The example code I gave works as is in Python2.
>
> The Python3 keyword only arguments are only syntactic sugar. See
> https://www.python.org/dev/peps/pep-3102 for the details. But, as the
> PEP notes,
>
> def f(a, b, *, key1, key2)
>
> is similar to doing this which also works in Python2
>
> def f(a, b, *ignore, key1, key2):
> if ignore:
> raise TypeError('too many positional arguments')
>
> For our case, we want to accept any number of positional arguments due
> to compatibility so we don't need or want the check for 'too many
> positional arguments'.
>
> Note that in both Python 2 and 3, invoking f(1, 2, key1='k1',
> key2='k2') is just syntactic sugar for constructing the (1, 2) tuple
> and {'key1': 'k1', 'key2': 'k2'} dict and passing those to f which
> then unpacks them into a, b, key1 and key2. You see that reflected in
> the C API where you get PyObject* args and PyObject* kw and you unpack
> them explicitly with PyArg_ParseTupleAndKeywords or just use tuple and
> dict calls to peek inside.
>
> What you loose by not having Python3 is that you can't use
> PyArg_ParseTupleAndKeywords and tell it that detail and so on are
> keywork only arguments. But because we don't want to unpack args we
> probably couldn't use that anyway even if we wouldn't support Python2.
>
> Therefore you need to look inside the kw dictionary manually as my
> example shows. What we could also do is check that the kw dictionary
> *only* contains detail, hint and so on and raise a TypeError if it has
> more things to avoid silently accepting stuff like:
> plpy.error('message', some_param='abc'). In Python3
> PyArg_ParseTupleAndKeywords would ensure that, but we need to do it
> manually.
>

It looks like good idea. Last version are not breaking compatibility - and
I think so it can works.

I wrote the code, that works on Python2 and Python3

Regards

Pavel