1、
>>> a = [] >>> b = ["aa","bb","cc"] >>> if len(a) == 0: print("empty!") empty!
>>> if len(b) == 0: print("empty!")
2、
>>> a = ["aa","bb","cc","dd"] >>> for i in a: print(i) else: print("empty!") aa bb cc dd empty!
>>> if a: ## 需要加if a for i in a: print(i) else: print("empty!") aa bb cc dd
>>> a = [] >>> for i in a: print(i) else: print("empty!") empty!
>>> if a: ## 正確 for i in a: print(i) else: print("empty!") empty!
3、
>>> a = ["aa","bb","cc","dd"] >>> if len(a) != 0: for i in a: print(i) else: print("empty!") aa bb cc dd >>> a = [] >>> if len(a) != 0: for i in a: print(i) else: print("empty!") empty!