[Python-3000] PEP 3101 Updated

[Eric Smith]

Ron Adam wrote:
>> I've been re-reading the PEP, in an effort to make sure everything is 
>> working.  I realized that these tests should not pass.  The PEP says 
>> that "Format specifiers can themselves contain replacement fields".  
>> The tests above have replacement fields in the field name, which is 
>> not allowed.  I'm going to remove this functionality.
>>
>> I believe the intent is to support a replacement for:
>> "%.*s" % (4, 'how now brown cow')
>>
>> Which would be:
>> "{0:.{1}}".format('how now brown cow', 4)
>>
>> For this, there's no need for replacement on field name.  I've taken 
>> it out of the code, and made these tests in to errors.
> 
> I think it should work myself, but it could be added back in later if 
> there is a need to.
> 
> 
> I'm still concerned about the choice of {{ and }} as escaped brackets.
> 
> What does the following do?
> 
> 
> "{0:{{^{1}}".format('Python', '12')

 >>> "{0:{{^{1}}".format('Python', '12')
Traceback (most recent call last):
   File "<stdin>", line 1, in <module>
ValueError: unterminated replacement field

But:
 >>> "{0:^{1}}".format('Python', '12')
'   Python   '

> "{{{0:{{^{1}}}}".format('Python', '12')
 >>> "{{{0:{{^{1}}}}".format('Python', '12')
Traceback (most recent call last):
   File "<stdin>", line 1, in <module>
ValueError: Unknown conversion type }

But,
 >>> "{{{0:^{1}}".format('Python', '12')
'{   Python   '

> class ShowSpec(str):
>     	
>     return spec
> 
> ShowSpec("{0:{{{1}}}}").format('abc', 'xyz')
> 

 >>> ShowSpec("{0:{{{1}}}}").format('abc', 'xyz')
Traceback (most recent call last):
   File "<stdin>", line 1, in <module>
ValueError: Invalid conversion specification

I think you mean:
ShowSpec("{0:{1}}").format('abc', 'xyz')

But I have some error with that.  I'm looking into it.

> "{0}".format('{value:{{^{width}}', width='10', value='Python')

 >>> "{0}".format('{value:{{^{width}}', width='10', value='Python')
'{value:{{^{width}}'