two generators working in tandem

[Michael Spencer]

john peter wrote:
> I'd like to write two generators: one is a min to max sequence number generator that
>   rolls over to min again once the max is reached. the other is a generator that cycles
>   through N (say, 12) labels. currently, i'm using these generators in nested loops like
>   this:
>    
>   seq_numbers = genSeqNum(min,max)
>   for label in genLabel():
>      for some_date in genDate(init):
>         for i in xrange(0, LIMIT):
>            print label, some_date, i, seq_numbers.next()
>    
>   The problem I'm trying to solve is this:
>   when the seq_numbers generator rolls over, the label generator must be advanced
>   to the next one "in tandem". does anyone has any suggestion? thanks for any hepl!
> 
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> 
This returns an iterator that 'nests' an arbitrary number of sequences 
(odometer-style).

def nest(*sequences):
     def _nest(outer, inner):
         for outer_item in outer:
             if not isinstance(outer_item, tuple):
                 outer_item = (outer_item,)
             for inner_item in inner:
                 yield outer_item + (inner_item,)
     return reduce(_nest, sequences)


So, for your use case:

  >>> seq_numbers = range(1,10)
  >>> labels = ["A","B","C"]
  >>> list(nest(labels, seq_numbers))
  [('A', 1), ('A', 2), ('A', 3), ('A', 4), ('A', 5), ('A', 6), ('A', 7), ('A', 
8), ('A', 9), ('B', 1), ('B', 2), ('B', 3), ('B', 4), ('B', 5), ('B', 6), ('B', 
7), ('B', 8), ('B', 9), ('C', 1), ('C', 2), ('C', 3), ('C', 4), ('C', 5), ('C', 
6), ('C', 7), ('C', 8), ('C', 9)]
  >>>


HTH, Michael