> PEP 318 is likely to change the BNF productions for funcdef,
> so I was taking a look at what is there right now.
>
> funcdef ::= "def" funcname "(" [parameter_list] ")" ":" suite
> parameter_list ::= (defparameter ",")*
> ("*" identifier [, "**" identifier] |
> "**" identifier | defparameter [","])
> defparameter ::= parameter ["=" expression]
> sublist ::= parameter ("," parameter)* [","]
> parameter ::= identifier | "(" sublist ")"
> funcname ::= identifier
>
> But the text points out that no purely positional (without a
> default value) arguments can occur after any keyword arguments.
> Is there a reason not to include this in the BNF?
>
> (Assuming the other productions are unchanged,) this seems to work:
>
> parameter_list ::= starparameter |
> defparameter ("," defparameter)* ["," [starparameter]] |
> parameter ("," parameter)* ("," defparameter)* ["," [starparameter]]
>
> starparameter ::= "*" identifier [, "**" identifier] |
> "**" identifier
>
> defparameter ::= parameter "=" expression
This can't work (at least not in the parser -- I don't care what's put
in the docs) because parameter and defparameter have the same set of
initial tokens.
> starparameter was separated out because a trailing comma is permitted
> after a positional or default parameter, but not after *args or **kwargs.
>
> Is there some technical reason not to do this?
Not to do what? Allow a comma after *args?
> For instance, is the doco autogenerated from the actual code?
You should know by now that there are various tools for that, although
again maybe you're asking the question in a different context.
> Is it somehow cheaper to check for an optional first parameter than
> for three possibilities?
Who cares?
--Guido van Rossum (home page: http://www.python.org/~guido/)
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