[Python-Dev] Backporting PEP 3101 to 2.6

[Eric Smith]

Steve Holden wrote:
> Nick Coghlan wrote:
>> To elaborate on this a bit (and handwaving a lot of important details 
>> out of the way) do you mean something like the following for the builtin 
>> format?:
>>
>> def format(obj, fmt_spec=None):
>>      if fmt_spec is None: fmt_spec=''
>>      result = obj.__format__(fmt_spec)
>>      if isinstance(fmt_spec, unicode):
>>          if isinstance(result, str):
>>              result = unicode(result)
>>      return result
>>
> Isn't unicode idempotent? Couldn't
> 
>           if isinstance(result, str):
>               result = unicode(result)
> 
> 
> avoid repeating in Python a test already made in C by re-spelling it as
> 
>          result = unicode(result)
> 
> or have you hand-waved away important details that mean the test really 
> is required?

This code is written in C.  It already has a check to verify that the 
return from __format__ is either str or unicode, and another check that 
fmt_spec is str or unicode.  So doing the conversion only if result is 
str and fmt_spec is unicode would be a cheap decision.

Good catch, though.  I wouldn't have thought of it, and there are parts 
that are written in Python, so maybe I can leverage this elsewhere.  Thanks!

Eric.