[Tutor] List index usage: is there a more pythonesque way?

bob gailer bgailer at gmail.com
Mon Apr 19 01:34:13 CEST 2010

On 4/18/2010 6:53 PM, C M Caine wrote:
> # Example data for forms and timetable:
> forms = ["P7", "P8", "P9", "P10", "P11", "S7", "S8", "S9", "S10",
> "S11", "IMA", "CAT", "FOR", "RLS", "EMPTY"]
> timetable = ['CAT', 'P10', 'P8', 'EMPTY', 'EMPTY', 'EMPTY', 'S10',
> 'S8', 'IMA', 'EMPTY', 'S7', 'S10', 'P9', 'EMPTY', 'EMPTY', 'EMPTY',
> 'S7', 'EMPTY', 'EMPTY', 'RLS', 'FOR', 'EMPTY', 'EMPTY', 'EMPTY', 'S9',
> 'EMPTY', 'EMPTY', 'S8', 'IMA', 'S11', 'P8', 'EMPTY', 'IMA', 'EMPTY',
> 'EMPTY', 'S11', 'S11', 'EMPTY', 'EMPTY', 'EMPTY', 'P7', 'S9', 'P11',
> 'EMPTY', 'EMPTY', 'P9', 'EMPTY', 'EMPTY', 'P8', 'FOR', 'S10', 'S11',
> 'S7', 'P7', 'EMPTY', 'EMPTY', 'IMA', 'EMPTY', 'S9', 'P10', 'P11',
> 'CAT', 'S8', 'P9', 'RLS']
> def analyseTimetable():
>          "Find number of and spaces between each form."

Consider using defaultdict in the collections module. The first time a 
key is referenced it is automatically added with a specified value.


import collections
          numDict = collections.defaultdict(0)
          spaceDict = collections.defaultdict(0)

>          adjustedSpaceDict = {}

If you use enumerate then you can replace timetable[i] with key
>          for i, key in enumerate(timetable):
>              numDict[key] += 1

Something is wrong in the following if statement, as both paths execute 
the same code.

>              if spaceDict['1st'+key] == 0:
>                  spaceDict['nth'+key] = i
>              else:
>                  spaceDict['nth'+key] = i
>          for form in forms:
>              adjustedSpaceDict[form] = spaceDict['nth'+form] - \
>                                        spaceDict['1st'+form]
>          return (numDict, adjustedSpaceDict)
> # End example
> This function works fine, but I think that using range(len(timetable))
> is clumsy. On the other hand, I need the indexes to track the number
> of spaces between instances of each form. Without using another loop
> (so not using list.index), is there a way of getting the index of the
> list entries?

Bob Gailer
Chapel Hill NC

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