Python類型錯誤 - 類型錯誤：'<'不支持'NoneType'和'int'的實例

Question

TypeError: '<' not supported between instances of 'NoneType' and 'int'

我在Stack Overflow找了個答案，發現我應該帶一個int（輸入（提示符） ），但是這就是我是做

def main():  
while True: 
     vPopSize = validinput("Population Size: ") 
     if vPopSize < 4: 
      print("Value too small, should be > 3") 
      continue 
     else: 
      break 

def validinput(prompt): 
while True: 
    try: 
     vPopSize = int(input(prompt)) 
    except ValueError: 
     print("Invalid Entry - try again") 
     continue 
    else: 
     break 

Answer 1

Try: 
    def validinput(prompt): 
    print(prompt) # this one is new!! 
    while True: 
     try: 
      vPopSize = int(input(prompt)) 
     except ValueError: 
      print("Invalid Entry - try again") 
      continue 
     else: 
      break 

而當函數被調用時，你會發現。

問題是validinput（）不會返回任何東西。你不得不返回vPopSize

Answer 2

，你需要在你的函數添加一回，讓你輸入的號碼，否則它返回一個隱含的無

def validinput(prompt): 
    while True: 
     try: 
      return int(input(prompt)) 
      # there is no need to use another variable here, just return the conversion, 
      # if it fail it will try again because it is inside this infinite loop 
     except ValueError: 
      print("Invalid Entry - try again") 


def main():  
    while True: 
     vPopSize = validinput("Population Size: ") 
     if vPopSize < 4: 
      print("Value too small, should be > 3") 
      continue 
     else: 
      break 

或在評論中指出，讓ValidInput的還檢查它是否是一個合適的值

def validinput(prompt): 
    while True: 
     try: 
      value = int(input(prompt)) 
      if value > 3: 
       return value 
      else: 
       print("Value too small, should be > 3") 
     except ValueError: 
      print("Invalid Entry - try again") 


def main():  
    vPopSize = validinput("Population Size: ") 
    # do stuff with vPopSize