Combining two sorted lists

Question

I'm just hoping if there's a way to simplify this recursive code that takes 2 sorted lists and combines the two together in a sorted manner (without actually having to re-sort them).

def merge (l1,l2):
 if len(l1) == 0 and len(l2) == 0:
 return []
 if len(l1) == 0:
 return l2
 if len(l2) == 0:
 return l1
 if l1[0] <= l2[0]:
 return [l1[0]] + merge(l1[1:], l2)
 if l2[0] <= l1[0]:
 return [l2[0]] + merge(l1, l2[1:])

Answer 1

Use the built-in heapq.merge:

heapq.merge(*iterables)

Merge multiple sorted inputs into a single sorted output (for example, merge timestamped entries from multiple log files). Returns an iterator over the sorted values.