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I admit I spent the first half of the email scratching my head and trying to figure out what NULL had to do with argument clinic specs. (Maybe it would mean that if the argument is "not given" in some appropriate way then we set the corresponding C variable to NULL?) Finding out you were talking about None came as a surprising twist.
-n
On 4 Aug 2014 08:13, "Larry Hastings" <larry@hastings.org> wrote:
Argument Clinic "converters" specify how to convert an individual argument to the function you're defining. Although a converter could theoretically represent any sort of conversion, most of the time they directly represent types like "int" or "double" or "str".
Because there's such variety in argument parsing, the converters are customizable with parameters. Many of these are common enough that Argument Clinic suggests some standard names. Examples: "zeroes=True" for strings and buffers means "permit internal \\0 characters", and "bitwise=True" for unsigned integers means "copy the bits over, even if there's overflow/underflow, and even if the original is negative".
A third example is "nullable=True", which means "also accept None for this parameter". This was originally intended for use with strings (compare the "s" and "z" format units for PyArg\_ParseTuple), however it looks like we'll have a use for "nullable ints" in the ongoing Argument Clinic conversion work.
Several people have said they found the name "nullable" surprising, suggesting I use another name like "allow\_none" or "noneable". I, in turn, find their surprise surprising; "nullable" is a term long associated with exactly this concept. It's used in C# and SQL, and the term even has its own Wikipedia page:
http://en.wikipedia.org/wiki/Nullable\_typeMost amusingly, Vala \*used\* to have an annotation called "(allow-none)", but they've broken it out into two annotations, "(nullable)" and "(optional)".
http://blogs.gnome.org/desrt/2014/05/27/allow-none-is-dead-long-live-nullable/
Before you say "the term 'nullable' will confuse end users", let me remind you: this is not user-facing. This is a parameter for an Argument Clinic converter, and will only ever be seen by CPython core developers. A group which I hope is not so easily confused.
It's my contention that "nullable" is the correct name. But I've been asked to bring up the topic for discussion, to see if a consensus forms around this or around some other name.
Let the bike-shedding begin,
/arry
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