New Python 3.0 string formatting - really necessary?

MRAB google at mrabarnett.plus.com
Sun Dec 21 03:49:57 CET 2008


Aaron Brady wrote:
> On Dec 20, 7:38 pm, Steven D'Aprano <st... at REMOVE-THIS-
> cybersource.com.au> wrote:
>> Instead of just whinging, how about making a suggestion to fix it? Go on,
>> sit down for an hour or ten and try to work out how a BINARY OPERATOR
>> like % (that means it can only take TWO arguments) can deal with an
>> arbitrary number of arguments, *without* having any special cases.
>>
>> Go on. Take your time. I'll be waiting.
> 
> Hi, not to take sides, but, there is a possibility.
> 
> This behavior is currently legal:
> 
>>>> "%i %%i" % 0 % 1
> '0 1'
> 
> So, just extend it.  (Unproduced.)
> 
>>>> "%i %i" % 0 % 1
> '0 1'
>>>> "%r %i" % (2, 3, 4) % 1
> '(2, 3, 4) 1'
>>>> "%r %i" % (2, 3, 4)
> '(2, 3, 4) %i'
> 
> Which is quite clever and way ahead of its (posessive) time.
> 
A couple of problems:

1. How do you handle a literal '%'? If you just double up then you'll 
need to fix the string after all your substitutions.

2. What if a substitution introduces a '%'?

I suppose a possible solution would be to introduce a special format 
string, including a literal, eg:

     f"%r %i" % (2, 3, 4) % 1

and then convert the result to a true string:

     print(str(f"%r %i" % (2, 3, 4) % 1))

(although print() would call __str__ anyway).

The format string would track where the last substitution occurred.

Hmm... I think I'll just learn the new method. :-)



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