extracting keywords from %(keyword)s-based templates

[Andrew Dalke]

Jeff Shannon wrote:
>Well, I *did* test this... I threw the above class into a module with:
>
>def test():
>    trap = KeywordTrap()
>    "Testing ... %d %s %f %(one) %(two) %(test)" % trap

Technically, the subject is
  'extracting keywords from %(keyword)s-based templates'
 :)

The '%d' syntax only works with a single object or a tuple, and
only tuples work if you have more than one positional % term.
The '%()s' syntax works different.

>So I tried getting rid of the %d %s etc, and just using the keyword
>formats...

>    "Testing ...  %(one) %(two) %(test)" % trap
>ValueError: incomplete format

Should be
     "Testing ...  %(one)s %(two)d %(test)f" % trap
                        ^^^     ^^^      ^^^

>Bummer.  Maybe we'd have to inherit from UserDict?  I haven't messed
>around with that at all...

Nope.  The % operator used by a string only needs the __getitem__
when given a '%()s' syntax.

For real fun, explain why this should work:

>>> class Spam:
...   def __getitem__(self, name):
...     return len(name)
...   def __int__(self):
...     return 987
...
>>> spam = Spam()
>>> "%d %(four)s %(yummy)s" % spam
'987 4 5'
>>>

Now I'm wondering in 2.2 what happens if I derive from ()...

                    Andrew
                    dalke at dalkescientific.com