[Python-ideas] Positional only arguments

[Aaron Brady]

> -----Original Message-----
> From: python-ideas-bounces at python.org [mailto:python-ideas-
> bounces at python.org] On Behalf Of George Sakkis
> def foo(a, b=42,           # pos-only
>              % ,                   # delimiter
>              c=0, d=None, # pos-or-kw
>              *args,              # varargs
>              e=-1,z='',        # kw-only
>              **kwds            # keyword dictionary
> )
> 
> Pros:
> - Backwards compatible: args are pos-or-kw by default as they are now;
> only those before the new delimiter are positional.
> - Easy to change the status of a parameter; just move it to the
> appropriate section (at least if it has a default value).
> 
> Cons:
> - Yet another magic symbol, smells like perl (reusing the single star
> would be ambiguous).
> - The presumably common cases of functions without pos-or-kw args is
> clumsy:
> def foo(a, b, c=31, %):  # all pos-only
> def bar(a, b=1, %, *, c=31, d=None):  # pos-only or kw-only
> 
> Overall, I still prefer the double underscores.
> 
> George
> 

One of the things I like about Python is we've got some extra room in the
syntax to complexify.  Careful how we spend it.  The extra is on a budget,
not unlimited as some things are.

def foo(a, b=42;           # pos-only
             c=0, d=None, # pos-or-kw
             *args;          # varargs
             e=-1,z='',        # kw-only
             **kwds            # keyword dictionary
)

def foo(a, b, c=31; ):  # all pos-only
def bar(a, b=1;; c=31, d=None):  # pos-only or kw-only

> - Yet another magic symbol, smells like perl (reusing the single star
> would be ambiguous).

True dat.