in place list modification necessary? What's a better idiom?

R. David Murray rdmurray at bitdance.com
Tue Apr 7 13:47:26 CEST 2009


"andrew cooke" <andrew at acooke.org> wrote:
> Carl Banks wrote:
> > import collections
> > import itertools
> >
> > def createInitialCluster(fileName):
> >     fixedPoints = []
> >     # quantization is a dict that assigns sequentially-increasing
> > numbers
> >     # to values when reading keys that don't yet exit
> >     quantization = defaultdict.collections(itertools.count().next)
> >     with open(fileName, 'r') as f:
> >         for line in f:
> >             dimensions = []
> >             for s in line.rstrip('\n').split(","):
> >                 if isNumeric(s):
> >                     dimensions.append(float(s))
> >                 else:
> >                     dimensions.append(float(quantization[s]))
> >             fixedPoints.append(Point(dimensions))
> >     return Cluster(fixedPoints)
> 
> nice reply (i didn't know defaultdict worked like that - very neat).
> 
> two small things i noticed:
> 
> 1 - do you need a separate quantization for each column?  the code above
> might give, for example, non-contiguous ranges of integers for a
> particular column if a string occurs ("by accident" perhaps) in more than
> one.
> 
> 2 - don't bother with isNumeric.  just return the cast value or catch the
> exception:
> 
>   [...]
>   try:
>     dimensions.append(float(s))
>   except:
>     dimensions.append(float(quantization[s]))

No, no, no; never use a bare except! :)

Do it MRAB's way and catch ValueError.

--
R. David Murray             http://www.bitdance.com




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