Source Code for Module TEES.Utils.Libraries.combine

 1  """ 
 2  Combinations from multiple sequences 
 3   
 4  Source: ASPN: Python Cookbook 
 5  Title: Generating combinations of objects from multiple sequences 
 6  Submitter: David Klaffenbach (other recipes) 
 7  Last Updated: 2004/08/29 
 8  Version no: 1.0 
 9  Category: Algorithms 
10   
11  Description: 
12   
13  The function combine takes multiple sequences and creates a list in which 
14  each item is constructed from items from each input sequence, and all possible 
15  combinations are created. If that description is confusing, look at the  
16  example in the docstring. It's a pretty simple transformation. The function  
17  xcombine is similar, but returns a generator rather than creating the output  
18  all at once. 
19  """ 
20   
21 -def combine(*seqin): 
22      '''returns a list of all combinations of argument sequences. 
23      for example: combine((1,2),(3,4)) returns 
24      [[1, 3], [1, 4], [2, 3], [2, 4]]''' 
25      def rloop(seqin,listout,comb): 
26          '''recursive looping function''' 
27          if seqin:                       # any more sequences to process? 
28              for item in seqin[0]: 
29                  newcomb=comb+[item]     # add next item to current comb 
30                  # call rloop w/ rem seqs, newcomb 
31                  rloop(seqin[1:],listout,newcomb) 
32          else:                           # processing last sequence 
33              listout.append(comb)        # comb finished, add to list 
34      listout=[]                      # listout initialization 
35      rloop(seqin,listout,[])         # start recursive process 
36      return listout 
37   
38 -def xcombine(*seqin): 
39      '''returns a generator which returns combinations of argument sequences 
40      for example xcombine((1,2),(3,4)) returns a generator; calling the next() 
41      method on the generator will return [1,3], [1,4], [2,3], [2,4] and 
42      StopIteration exception.  This will not create the whole list of  
43      combinations in memory at once.''' 
44      def rloop(seqin,comb): 
45          '''recursive looping function''' 
46          if seqin:                   # any more sequences to process? 
47              for item in seqin[0]: 
48                  newcomb=comb+[item]     # add next item to current combination 
49                  # call rloop w/ remaining seqs, newcomb 
50                  for item in rloop(seqin[1:],newcomb):    
51                      yield item          # seqs and newcomb 
52          else:                           # processing last sequence 
53              yield comb                  # comb finished, add to list 
54      return rloop(seqin,[]) 
55