def f(x): print 'original' if x > 0: return f(x-1) return 0 g = f def f(x): print 'new' return x print g(5) 结果是: original new 4 证明了: 1.when g(5) runs, origninal `f`is called,not new `f`.2.as 5>0,'return f(x-1)'is executed 3.new`f`is called when `f(x…