Python奇偶判断程序为何输出None？三种实现方法问题排查

问题根源 #

前两种方法出现None输出的核心原因是在三元表达式中直接调用了print()函数：

• print()函数执行时会输出内容，但它本身的返回值是None
• 当三元表达式走else分支时，变量会被赋值为None（或外层print()会接收这个None作为输出内容），最终导致额外的None被打印

修正后的代码实现 #

# 方法一：修正三元表达式逻辑，避免直接在分支里调用print
user_number = int(input("Please enter the number you want to check\n"))
message_to_print = "Your number is even" if user_number % 2 == 0 else "Your number is odd"
print(message_to_print)

# 方法二：同样修正三元表达式，将字符串作为分支结果而非调用print
user_number_check = (user_number / 2).is_integer()
print("Your number is even" if user_number_check else "Your number is odd")

# 方法三：原逻辑正常，无需修改
if user_number_check:
    print("Your number is even ")
elif not user_number_check:
    print("Your number is odd ")

额外优化建议 #

• 方法一中可以直接用三元表达式作为print()的参数，简化代码：

  print("Your number is even" if user_number % 2 == 0 else "Your number is odd")
  

• 方法二中判断奇偶性更高效的方式是用取模运算user_number % 2 == 0，比除法后判断是否为整数的性能更好

内容的提问来源于stack exchange，提问作者Rami DJEFFAL