[Tutor] numbers and ranges

Kent Johnson kent37 at tds.net
Sun May 27 22:33:05 CEST 2007

Jon Crump wrote:
> Dear all,
> Here's a puzzle that should be simple, but I'm so used to words that 
> numbers tend to baffle me.
> I've got fields that look something like this:
> 1942. Oct. 1,3,5,7,8,9,10
> I need to parse them to obtain something like this:
> <sometag start="1942-10-01"/>
> <sometag start="1942-10-03"/>
> <sometag start="1942-10-05"/>
> <sometag start="1942-10-07" end "1942-10-10"/>
> The xml representation is incidental, the basic problem is how to test a 
> list of integers to see if they contain a range, and if they do, do 
> something different with them.

Here is a solution that uses a generator to create the ranges:

def ranges(data):
     i = iter(data)
     first = last = i.next()
         while 1:
             next = i.next()
             if next > last+1:
                 yield (first, last)
                 first = last = next
                 last = next
     except StopIteration:
         yield (first, last)

print list(ranges((1,)))
print list(ranges((1,2,3)))
print list(ranges((1,3,5)))
print list(ranges((1,3,5,7,8,9,10)))

for start, end in ranges((1,3,5,7,8,9,10)):
     if start == end:
         print '<sometag start="1942-10-%02d"/>' % start
         print '<sometag start="1942-10-%02d" end "1942-10-%02d"/>' % 
(start, end)


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