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

[andrew cooke]

just playing around - doesn't work with 3.0 due to lack of pattern binding
(which i think is coming back in 3.1?)

>>> from collections import defaultdict
>>> from itertools import count
>>> def mkdict(): return defaultdict(count().next)
...
>>> converters = defaultdict(mkdict)
>>> def to_float((i, s)):
...   try: return float(s)
...   except: return converters[i][s]
...
>>> def convert(line):
...   return map(to_float, zip(count(), line.split(',')))
...
>>> convert('1,2,red')
[1.0, 2.0, 0]
>>> convert('1,2,red')
[1.0, 2.0, 0]
>>> convert('1,2,blue')
[1.0, 2.0, 1]
>>> convert('1,2,blue,blue')
[1.0, 2.0, 1, 0]


andrew cooke 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]))
>
> (not sure float() is needed there either if you're using a recent version
> of python - only reason i can think of is to avoid integer division in
> older versions).
>
> andrew
>
>
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>
>