#!/usr/bin/env python3
 
import timeit
 
def prepare1():
 
    def merge(left, right):
        """Merge two lists in ascending order."""
        lst = []
        while left and right:
            if left[0] < right[0]:
                lst.append(left.pop(0))
            else:
                lst.append(right.pop(0))
        if left:
            lst.extend(left)
        if right:
            lst.extend(right)
        return lst
 
    return merge
 
def prepare2():
 
    def merge(a,b):
        a, b = iter(a), iter(b)
        def gen(a, b):
            vb = next(b)
            try:
                while 1:
                    va = next(a)
                    if va > vb: va, vb, a, b = vb, va, b, a
                    yield va
            except: yield vb
        yield from gen(a, b)
        yield from a
        yield from b
 
    return merge
 
def prepare3():
 
    def merge(a,b):
        a, b = iter(a), iter(b)
        try:
            vb = next(b)
            try:
                while 1:
                    va = next(a)
                    if va > vb: va, vb, a, b = vb, va, b, a
                    yield va
            except: yield vb
            yield from b
        except: yield from a
 
    return merge
 
merge1 = prepare1()
merge2 = prepare2()
merge3 = prepare3()
 
lst1 = list(range(1, 100000, 2))
lst2 = list(range(2, 100001, 2))
lst11 = list(range(1, 100000, 2))
lst22 = list(range(2, 100001, 2))
lst111 = list(range(1, 100000, 2))
lst222 = list(range(2, 100001, 2))
 
def f1():
    merge1([], [])
    merge1([1, 3, 5], [2, 4, 6])
    merge1(lst1, lst2)
 
def f2():
    list(merge2([], []))
    list(merge2([1, 3, 5], [2, 4, 6]))
    list(merge2(lst11, lst22))
 
def f3():
    list(merge3([], []))
    list(merge3([1, 3, 5], [2, 4, 6]))
    list(merge3(lst111, lst222))
 
def main():
    t1 = timeit.Timer('f1()', 'from __main__ import f1')
    t2 = timeit.Timer('f2()', 'from __main__ import f2')
    t3 = timeit.Timer('f3()', 'from __main__ import f3')
     
    for t in t1, t2, t3:
        print(t.repeat(3, 100))
 
if __name__ == '__main__':
    main()

[guest@localhost py]$ ./mergecmp1.py 
[0.6375549949998458, 0.0005647759999192203, 0.0005668369994964451]
[4.651441780999448, 4.622966723999525, 4.6205978140005755]
[3.620450236000579, 3.6205695090002337, 3.611680899000021]
[guest@localhost py]$