[Python-ideas] String formatting and namedtuple

[Georg Brandl]

Guido van Rossum schrieb:
> On Mon, Feb 16, 2009 at 12:48 AM, Christian Tanzer <tanzer at swing.co.at> wrote:
>> A fair amount of my use cases involve a non-literal format string
>> (i.e., passed in as argument, defined as module or class variable, or
>> even doc-strings used as format strings). I'd guess that most
>> non-literal format strings are used together with dictionaries.
>>
>> Unfortunately, it's hard to grep for this :-(, so I can't give you
>> hard numbers.
> 
> It would be pretty simple to rig up 2to3 to report any string literals
> containing e.g. '%(...)s' that are not immediately followed by a %
> operator.

The major problems I see are

1) __mod__ application with a single right-hand operand (a tuple makes it
   a string formatting to 100%, at least without other types overloading %)
2) format strings coming from external sources

The first can't be helped easily.  For the second, a helper function that
converts %s format strings to {0} format strings could be imagined.  A call
of the form

   fmtstr % (a, b)

would then be converted to

   _mod2format(fmtstr).format(a, b)

To fix 1), _mod2format could even return a wrapper that executes .__mod__
on .format() if fmtstr is not a string. <half-wink>

>> Another, probably fairly common, use case involving non-literal
>> strings is %-formatting in I18N strings -- though it might be possible
>> to fix these automatically.
> 
> Plus, i18n is one of the motivators for .format() -- less chance of
> forgetting to type the trailing 's' in '%(foobar)s' and the ability to
> rearrange positional arguments a la "foo {1} bar {0} baz".

I expect future generations of translators will be thankful.  Current
generation may be angry when they have to revise their .po files :)

Georg

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