import heapq
def imerge(*iterables):
'''Merge multiple sorted inputs into a single sorted output.
Equivalent to: sorted(itertools.chain(*iterables))
>>> list(imerge([1,3,5,7], [0,2,4,8], [5,10,15,20], [], [25]))
[0, 1, 2, 3, 4, 5, 5, 7, 8, 10, 15, 20, 25]
'''
heappop, siftup, _StopIteration = heapq.heappop, heapq._siftup, StopIteration
h = []
h_append = h.append
for it in map(iter, iterables):
try:
next = it.next
h_append([next(), next])
except _StopIteration:
pass
heapq.heapify(h)
while 1:
try:
while 1:
v, next = s = h[0] # raises IndexError when h is empty
yield v
s[0] = next() # raises StopIteration when exhausted
siftup(h, 0) # restore heap condition
except _StopIteration:
heappop(h) # remove empty iterator
except IndexError:
return
if __name__ == '__main__':
import doctest
doctest.testmod()
