[Python-Dev] Rough idea for adding introspection information for builtins (original) (raw)

Ronald Oussoren ronaldoussoren at mac.com
Tue Mar 19 10:42:16 CET 2013

On 19 Mar, 2013, at 10:24, Larry Hastings <larry at hastings.org> wrote:

We'd want one more mild hack: the DSL will support positional parameters, and inspect.Signature supports positional parameters, so it'd be nice to render that information. But we can't represent that in Python syntax (or at least not yet!), so we can't let ast.parse see it. My suggestion: run it through ast.parse, and if it throws a SyntaxError see if the problem was a slash. If it was, remove the slash, reprocess through ast.parse, and remember that all parameters are positional-only (and barf if there are kwonly, args, or kwargs). It will be simpler to use some one-character separator which shouldn't be used unquoted in the signature. I.e. LF. I had trouble understanding what you're suggesting. What I think you're saying is, "normally these generated strings won't have LF in them. So let's use LF as a harmless extra character that means 'this is a positional-only signature'." At one point Guido suggested / as syntax for exactly this case. And while the LF approach is simpler programmatically, removing the slash and reparsing isn't terribly complicated; this part will be in Python, after all. Meanwhile, I suggest that for human readability the slash is way more obvious--having a LF in the string mean this is awfully subtle.

You could also add the slash to the start of the signature, for example "/(arg1, arg2)", that way the positional only can be detected without trying to parse it first and removing a slash at the start is easier than removing it somewhere along a signature with arbitrary default values, such as "(arg1='/', arg2=4 /) -> 'arg1/arg2'". The disadvantage is that you can't specify that only some of the arguments are positional-only, but that's not supported by PyArg_Parse... anyway.

Ronald

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