[PEP] matching and mismatching (fwd)

[Lulu of the Lotus-Eaters]

|There was a proposal to make 'generator comprehensions', with a syntax
|like
|    for x in [yield line in file if len(strip(line))]:
|	    print x
|but it was rejected.  (http://python.org/peps/pep-0289.html)

I think the same PEP discussed some lazy FP functions (I'm lazy now,
maybe it was a different PEP).  In any case, writing you own is really
easy:

    def xfilter(predicate, iterable):
        if predicate is None:       # Compat with filter()
            predicate = lambda: 1
        for item in iterable:
            if predicate(item):
                yield item

Once you have it, calling it without the need to read the whole list is
simple:

    for line in xfilter(lambda l: len(strip(l)), file):
        print line

Of course, the lambda is harder to read, better would be:

    def nonempty: return len(strip(l))
    for line in xfilter(nonempty, file):
        print line

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