Inspired by this recipe: http://code.activestate.com/recipes/576961/, I played a little with the code and came with a more general piece of code implementing recursive iterators.
Python, 51 lines
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Copy to clipboard1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 | from itertools import tee, izip, imap, chain, islice, groupby
from heapq import merge
class DeferredIterator(object):
def __iter__(self):
for v in self.iterator:
yield v
def setIterator(self, i):
self.iterator = i
class InfiniteSequence:
def __getitem__(self, idx):
if isinstance(idx, slice):
return islice(self, idx.start, idx.stop, idx.step)
else:
return next(islice(self, idx, idx+1))
class Fibonacci(InfiniteSequence):
def __iter__(self):
R = DeferredIterator()
all, p1, p2 = tee(R, 3)
results = chain ( [0], all )
zipped = izip(p1, chain([0], p2))
mapped = imap( lambda x: x[0]+x[1], zipped )
R.setIterator ( chain ( [1], (v for v in mapped) ) )
return results
class RegularNumbers(InfiniteSequence):
#Solutions to 2**i * 3**j * 5**k for some integers i, j and k
def __iter__(self):
R = DeferredIterator()
result, p2, p3, p5 = tee (R, 4)
m2 = (2*x for x in p2)
m3 = (3*x for x in p3)
m5 = (5*x for x in p5)
merged = merge(m2,m3,m5)
combined = chain([1], merged)
R.setIterator( (k for k,v in groupby(combined)) )
return result
fib = Fibonacci()
for f in fib[0:15]:
print f
reg = RegularNumbers()
for r in reg[0:15]:
print r
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