如何检查输入值是否为有效字符串？

Question

所以我做了一个游戏的刽子手，它开始与一个“僵尸大师”输入一个字符串，然后有多少猜测，玩家将不得不尝试猜测字符串。我只是刚刚开始，我正在尝试编写一个函数来检查BotMaster输入的内容是否是有效的字符串。一个有效的字符串应该是一个只有字母、没有符号、数字或额外空格的字符串。我已经有了一些函数，它们可以删除多余的空格和非alpha输入（因此它可以去掉句点、多余的空格等等），还有一个函数可以将它们全部小写，但是如果我输入一个数字或一个空字符串，我的函数就会中断。我该如何添加这些？你知道吗

#Imports (this is for later code I haven't written)
import os,time,random

#Removes extra spaces from the function
def space_cull(the_str):
  result = the_str 
  result = result.strip()
  result =" ".join(result.split())
  the_str = result
  return the_str

#Makes the string lowercase
def make_lower(the_str):
  the_str = the_str.lower()
  return the_str

#Checks if everything in the string are Alpha Inputs
def check_alpha(the_str):
  the_str =''.join([char for char in the_str if char.isalnum()])
  return the_str 

#Ask Botmaster the string they want
def ask_bot():
  while True:
   bot_str = input('Enter a string for the player to guess: ')
   bot_str = space_cull(bot_str)
   bot_str = make_lower(bot_str)
   bot_str = check_alpha(bot_str)
   if bot_str == '':
      print('That is not a correct string, try again')
      True
   return bot_str

ask_bot()

我添加了ask\u bot（）部分，以便更快地测试函数 事情就是这样：

Enter a string for the player to guess: 1
#nothing 
#Tested again:
Enter a string for the player to guess: ''
That is not a correct string, try again.
#But then exits the loop, which I don't want it to, if the string is wrong I want it to ask them again.
#Tested Again
Enter a string for the player to guess: 'Katze'
#Nothing, which is actually good this time

我该怎么解决这个问题？你知道吗

Answer 1

正如johngordon已经提到的，解决方案是“str”类的方法“isalpha”。你知道吗

userInput = input("Your suggestion: ")
if userInput.isalpha():
    # do some magic
else:
    print("please only type in letters")

Answer 2

You don't need the check_alpha(str) function at all. Modify the ask_bot() as follows.

def ask_bot():
  while True:
   bot_str = input('Enter a string for the player to guess: ')
   bot_str = space_cull(bot_str)
   bot_str = make_lower(bot_str)
   if not bot_str.isalpha():
     if bot_str.isnum():
       print("The entered string is a number")
       continue

     if bot_str == '':
       print('That is not a correct string, try again')
       continue

     continue

   break

return bot_str

询问\u bot（）

Answer 3

while循环在编写时总是在函数中终止。你知道吗

def ask_bot():
  while True:
   bot_str = input('Enter a string for the player to guess: ')
   bot_str = space_cull(bot_str)
   bot_str = make_lower(bot_str)
   bot_str = check_alpha(bot_str)
   if bot_str == '':
      print('That is not a correct string, try again')
      True # <- this does nothing
   return bot_str # < - this breaks out of the function and the loop

您的代码被编辑为工作：

def ask_bot():
  while True:
   bot_str = input('Enter a string for the player to guess: ')
   bot_str = space_cull(bot_str)
   bot_str = make_lower(bot_str)
   bot_str = check_alpha(bot_str)
   if bot_str == '':
      print('That is not a correct string, try again')
   else: # returns the string if the input is correct
      return bot_str # this still breaks out of the function and the loop
                     # but only if the string has passed the checks

正如其他答案已经提到的，你可以使用isalpha街（）若要检查字符串是否有效，或者如果要修改字符串，则需要调整check_alpha函数，如下所示：

def check_alpha(the_str):
  the_str =''.join([char for char in the_str if char.isalpha()])
  return the_str