Unanswered Questions in python.faqts.com

[Will Ware]

Charles Hixson (charleshixsn at earthlink.net) wrote:
> Unfortunately, the FAQTS question
> format caused an oversimplified question... my ideal form
> of the answer would allow a database to be merged into the language with
> btree access as the underlying format, and nominal form looking like a cross
> between a dictionary and a sequence.  I... want to slice on...
> key value (like a between query).
> I know that this is possible via subroutine calls, but I was wondering if
> there were any way that made more direct use of the preexisting syntax,
> e.g.:  abrasax = litmus {"acid" : "base"} or some such.

I'm not aware of any such thing. I tried hacking together a version of
__getslice__ that would take non-integer arguments, but alas, Python
checks the argument types before it passes them to __getslice__. This
means you need to define your own slicing operation. This seems to work:

import sys, types

class SeqDictHybrid:
    def __init__(self, keylist, valuelist):
        self.d = { }
        for k, v in map(None, keylist, valuelist):
            self.d[k] = v
        self.keylist = keylist
        self.valuelist = valuelist
    def myslice(self, i=0, j=sys.maxint):
        if type(i) != types.IntType:
            i = self.keylist.index(i)
        if type(j) != types.IntType:
            j = self.keylist.index(j)
        return self.valuelist[i:j]

litmus = SeqDictHybrid(['wayAcid', 'acid', 'neutral', 'base', 'wayBase'],
                       [5.0, 6.0, 7.0, 8.0, 9.0])   # pH, if I recall rightly

print litmus.myslice('acid', 'base')  --> [6.0, 7.0]

Adding btrees and clever insertions is an exercise left to the reader.

-- 
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# Resistance is futile. Capacitance is efficacious.
# Will Ware	email:    wware @ world.std.com