1 from greenlet import greenlet
 2 def test1():
 3     print(12)
 4     gr2.switch()
 5     print(34)
 6     gr2.switch()
 7 def test2():
 8     print(56)
 9     gr1.switch()
10     print(78)
11 gr1=greenlet(test1)
12 gr2=greenlet(test2)
13 gr1.switch()