完成此操作的最简单方法是将
input方法置于
while循环中。
continue当输入错误时使用，
break当你感到满意时使用。
当你的输入可能引发异常时
使用
try和
except检测用户何时输入了无法解析的数据。
while True: try: # Note: Python 2.x users should use raw_input, the equivalent of 3.x's input age = int(input("Please enter your age: ")) except ValueError: print("Sorry, I didn't understand that.") #better try again... Return to the start of the loop continue else: #age was successfully parsed! #we're ready to exit the loop. breakif age >= 18: print("You are able to vote in the United States!")else: print("You are not able to vote in the United States.")实施你自己的验证规则
如果要拒绝Python可以成功解析的值，则可以添加自己的验证逻辑。
while True: data = input("Please enter a loud message (must be all caps): ") if not data.isupper(): print("Sorry, your response was not loud enough.") continue else: #we're happy with the value given. #we're ready to exit the loop. breakwhile True: data = input("Pick an answer from A to D:") if data.lower() not in ('a', 'b', 'c', 'd'): print("Not an appropriate choice.") else: break结合异常处理和自定义验证
以上两种技术都可以组合成一个循环。
while True: try: age = int(input("Please enter your age: ")) except ValueError: print("Sorry, I didn't understand that.") continue if age < 0: print("Sorry, your response must not be negative.") continue else: #age was successfully parsed, and we're happy with its value. #we're ready to exit the loop. breakif age >= 18: print("You are able to vote in the United States!")else: print("You are not able to vote in the United States.")将其全部封装在一个函数中
如果你需要询问用户许多不同的值，则将此代码放在函数中可能很有用，因此你不必每次都重新键入。
def get_non_negative_int(prompt): while True: try: value = int(input(prompt)) except ValueError: print("Sorry, I didn't understand that.") continue if value < 0: print("Sorry, your response must not be negative.") continue else: break return valueage = get_non_negative_int("Please enter your age: ")kids = get_non_negative_int("Please enter the number of children you have: ")salary = get_non_negative_int("Please enter your yearly earnings, in dollars: ")放在一起
你可以扩展此思想，以创建非常通用的输入函数：
def sanitised_input(prompt, type_=None, min_=None, max_=None, range_=None): if min_ is not None and max_ is not None and max_ < min_: raise ValueError("min_ must be less than or equal to max_.") while True: ui = input(prompt) if type_ is not None: try: ui = type_(ui) except ValueError: print("Input type must be {0}.".format(type_.__name__)) continue if max_ is not None and ui > max_: print("Input must be less than or equal to {0}.".format(max_)) elif min_ is not None and ui < min_: print("Input must be greater than or equal to {0}.".format(min_)) elif range_ is not None and ui not in range_: if isinstance(range_, range): template = "Input must be between {0.start} and {0.stop}." print(template.format(range_)) else: template = "Input must be {0}." if len(range_) == 1: print(template.format(*range_)) else: print(template.format(" or ".join((", ".join(map(str, range_[:-1])),str(range_[-1]))))) else: return ui用法如下：
age = sanitised_input("Enter your age: ", int, 1, 101)answer = sanitised_input("Enter your answer: ", str.lower, range_=('a', 'b', 'c', 'd'))
