template strings for matching?

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    Tino> ??? can you elaborate? I don't see the problem.

    Tino> "%(foo)s" % mapping

Joe wants to go in the other direction.  Using your example, he wants a
function which takes a string and a template string and returns a dict.
Here's a concrete example:

    s = "My dog has fleas"
    fmt = "My $pet has $parasites"
    d = fmt_extract(fmt, s)
    assert d['pet'] == 'dog'
    assert d['parasites'] == 'fleas'

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