[Python-Dev] Re: Alternative Implementation forPEP292:SimpleString Substitutions

[Barry Warsaw]

On Fri, 2004-09-10 at 01:50, Raymond Hettinger wrote:
> [Barry]
> > And to make effbot and Raymond happy, it won't auto-promote to unicode
> > if everything's an 8bit string.
> 
> Glad to see that my happiness now ranks as a development objective ;-)

Well, if I want to get other work done... :)

> > There will be updated unit tests, and I will update the documentation
> > and the PEP as appropriate -- if we've reached agreement on it.
> 
> +1 
> Beautiful job.

Cool!

> The arguments against such reporting are:
> * Raymond is smoking crack.  End users will never make this mistake.
> * The docs say python identifiers only.  You blew it.  Tough.  Not a
> bug.
> * For someone who understands exactly what they are doing, perhaps $ma
> is the intended placeholder -- why force them to uses braces:
> ${ma}ñana.

It also makes it more difficult to document.  IOW, right now the PEP and
the documentation say that the first non-identifier character terminates
the placeholder.  How would you word the rules with your change?

> In addition to the above usability issue, there is one other nit.  The
> new invocation syntax offers us the opportunity for to also accept
> keyword arguments as mapping alternatives:
> 
>     def substitute(self, mapping=None, **kwds):
>         if mapping is None:
>            mapping == kwds
>      . . .
> 
> When applicable, this makes for beautiful, readable calls:
> 
>     t.substitute(who="Barry", what="mailmeister", when=now())
> 
> This would be a simple and nice enchancement to Barry's excellent
> implementation.  I recommend that keyword arguments be adopted.

My only problem with that is the interference that the 'mapping'
argument presents.  IOW, kwds can't contain 'mapping'.  We could solve
that in a couple of ways:

1. ignore the problem and tell people not to do that
2. change 'mapping' to something less likely to collide, such as
'_mapping' or '__mapping__', and then see #1.
3. get rid of the mapping altogether and only have kwds.  This would
change the non-keyword invocation from

mytemplate.substitute(mymapping)

to

mytemplate.substitute(**mymapping)

A bit uglier and harder to document.

Note that there's also a potential collision on 'self'.

-Barry

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