[Python-ideas] Keyword only argument on function call

[David Mertz]

>
> I disagree. Those are examples of people being used to *positional
> arguments* and this expecting that order to carry over. I don’t think
> that’s a good argument because it presupposes that a habit of positional
> arguments is good.
>

If 99% of existing code uses:

    pd.read_csv(fname, parse_dates=True, day_first=True)

In preference to:

    pd.read_csv(fname, day_first=True, parse_dates=True)

It seems pretty absurd to say that readability isn't harmed by someone
choosing the "non-standard" order.  Of course it still works the same for
the library; but it's not the same for humans reading the code.

There is one thing: my proposal wouldn’t result in a NameError at the
> eval() call. You tried it out in a console but didn’t think about the
> scoping properly. For your suggestion to work you have to copy paste that
> helper function into the code at all scopes you want to use it.
>

This is just wrong.  Assuming there is no 'd' available in the current
scope, what could this POSSIBLY do other than raise a NameError:

    function(a=77, *, b, d)

My little utility function decided to convert the NameError into a None
value for the missing variable; but I mentioned that I'm not sure whether
that's more useful behavior, and I'm not much attached to one or the other.

    function(a=77, **use('b d'))

To make that helper function work you need to grab the stack frame and
> extract the variables from there. You could absolutely do that though.
> That’s pretty evil though.
>

Nope, there's absolutely no need to poke into the stack frame.  It's just a
regular closure over any variables that might exist in surrounding scopes.
*Exactly* the same thing that your proposal would have to do.  It makes
absolutely no difference how deeply or shallowly nested the call to `use()`
might be... A name like `d` simply is or is not available. Since the
utility function doesn't have its own locals or formal parameters, nothing
is changed by being one level deeper.[*]

[*] Actually, that's not true.  My implementation potentially steps on the
three names `names`, `name` and `kws`.  Perhaps those should be called
`__names`, `__name`, and `__kws` to avoid that issue.  If so, that's an
easy change.


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