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import itertools
def xcombine(*seqin):
'''returns a generator which returns combinations of argument sequences
for example xcombine((1,2),(3,4)) returns a generator; calling the next()
method on the generator will return [1,3], [1,4], [2,3], [2,4] and
StopIteration exception. This will not create the whole list of
combinations in memory at once.'''
def rloop(seqin,comb):
'''recursive looping function'''
if seqin: # any more sequences to process?
for item in seqin[0]:
newcomb=comb+[item] # add next item to current combination
# call rloop w/ remaining seqs, newcomb
for item in rloop(seqin[1:],newcomb):
yield item # seqs and newcomb
else: # processing last sequence
yield comb # comb finished, add to list
return rloop(seqin,[])
def cartn(sequence, n):
tocombine=list(itertools.repeat(sequence,n))
return itertools.imap(tuple,xcombine(*tocombine))
if __name__=='__main__':
for i in cartn([1,2,3],4):
print i
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