On 10/31/2010 6:28 PM, Glenn Linderman wrote:
On 10/31/2010 2:02 PM, Benjamin Peterson wrote:
2010/10/31 Antoine Pitrou<solip...@pitrou.net>:
>  On Sun, 31 Oct 2010 16:39:44 -0400
>  Eric Smith<e...@trueblade.com>  wrote:
>
>>  What are your thoughts on adding a str.format_from_mapping (or similar
>>  name, maybe the suggested "format_map") to 3.2? See
>>  http://bugs.python.org/issue6081  . This method would be similar to
>>  "%(foo)s %(bar)s" % d, where d is a dict (or rather any mapping object),
>>  but of course would use str.format syntax: "{foo}
>>  {bar}".format_from_mapping(d).
>
>  I must be missing something, but what's the difference with
>  XXX.format(**d)?
It allows arbitrary mappings.

Other than the language moratorium, why are arbitrary mappings not
allowed for the (**d) syntax?

An arbitrary mapping would be converted to a dict. That disallows using a subclass with __missing__ defined, among other things. See the discussion in the issue.
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