结束用户输入的Python程序

Question

我正在尝试使用用户输入来结束程序。我希望他们只需点击当他们需要退出时输入。我究竟做错了什么？

# 1)Pace.py 
# Converts miles per hour to minutes per mile. 

print ("Hello! This program will convert the miles per hour you got on your treadmill to >minutes per mile.") # Greeting 

def main() : # Defines the function main 

    while True : # The loop can repeat infinitely for multiple calculations. 
     mph = eval (input ("Please enter your speed in miles per hour. ")) # Asks for >user input and assigns it to mph. 
     mpm = 1/(mph/60) # The user input is divided by 60, and that is divided by 1. >This is assigned to mpm. 
     print ("Your speed was", mpm, "minutes per mile!") # Prints out the miles per >minute. 
     if mph == input ("") : # If the user entered nothing... 
      break # ...The program stops 
main() # Runs main. 

Answer 1

if not mph将捕获一个空字符串作为输入并结束您的循环。

在检查空字符串作为输入之后，请勿使用eval强制转换为int。

def main() : # Defines the function main 
    while True : # The loop can repeat infinitely for multiple calculations. 
     mph = (input ("Please enter your speed in miles per hour or hit enter to exit. ")) # Asks for >user input and assigns it to mph. 
     if not mph: # If the user entered nothing... 
      break # ...The program stops 
     mpm = 1/(int(mph)/60) # The user input is divided by 60, and that is divided by 1. >This is assigned to mpm. 
     print ("Your speed was", mpm, "minutes per mile!") # Prints out the miles per >minute. 
main() # Runs main. 

您应该使用try/except赶不正确的输入，以避免ValueError并检查英里是> 0，以避免ZeroDivisionError：

def main() : # Defines the function main 
    while True : # The loop can repeat infinitely for multiple calculations. 
     mph = (raw_input ("Please enter your speed in miles per hour. ")) # Asks for >user input and assigns it to mph. 
     if not mph: # If the user entered nothing... 
      break # ...The program stops 
     try: 
      mpm = 1/(int(mph)/60.) # The user input is divided by 60, and that is divided by 1. >This is assigned to mpm. 
     except (ZeroDivisionError,ValueError): 
      print("Input must be an integer and > 0") 
      continue 
     print ("Your speed was", mpm, 
     "minutes per mile!") # Prints out the miles per >minute. 
main() # Runs main.