问题:要求用户提供输入,直到他们给出有效的答复

我正在编写一个接受用户输入的程序。

#note: Python 2.7 users should use `raw_input`, the equivalent of 3.X's `input`
age = int(input("Please enter your age: "))
if age >= 18: 
    print("You are able to vote in the United States!")
else:
    print("You are not able to vote in the United States.")

只要用户输入有意义的数据,该程序就会按预期运行。

C:\Python\Projects> canyouvote.py
Please enter your age: 23
You are able to vote in the United States!

但是如果用户输入无效数据,它将失败:

C:\Python\Projects> canyouvote.py
Please enter your age: dickety six
Traceback (most recent call last):
  File "canyouvote.py", line 1, in <module>
    age = int(input("Please enter your age: "))
ValueError: invalid literal for int() with base 10: 'dickety six'

除了崩溃,我希望程序再次请求输入。像这样:

C:\Python\Projects> canyouvote.py
Please enter your age: dickety six
Sorry, I didn't understand that.
Please enter your age: 26
You are able to vote in the United States!

我如何使程序要求输入有效信息,而不是在输入无意义的数据时崩溃?

我该如何拒绝像-1这样的值,该值是有效的int,但在这种情况下是荒谬的?

标签:python,validation,loops,python-3.x,user-input

回答1:

最简单的方法是将input方法放入while循环中。使用 输入错误时继续 ,并在满意时中断

当您的输入可能引发异常时

使用 tryexcept 来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.
        break
if age >= 18: 
    print("You are able to vote in the United States!")
else:
    print("You are not able to vote in the United States.")

实施您自己的验证规则

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.
        break

while 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.
        break
if age >= 18: 
    print("You are able to vote in the United States!")
else:
    print("You are not able to vote in the United States.")

将其全部封装在函数中

如果您需要询问用户许多不同的值,则可以将此代码放入函数中,因此不必每次都重新输入。

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 value

age = 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: ")

将它们放在一起

您可以将这个想法扩展为一个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'))

常见陷阱以及为什么要避免它们

冗余使用input语句

此方法有效,但通常被认为是较差的样式:

data = input("Please enter a loud message (must be all caps): ")
while not data.isupper():
    print("Sorry, your response was not loud enough.")
    data = input("Please enter a loud message (must be all caps): ")

最初看起来很有吸引力,因为它比whileTrue方法短,但是它违反了不要重复自己的软件开发原理。这增加了系统中错误的可能性。如果您想通过将input更改为raw_input来反向移植到2.7,而又意外地仅更改了上面的第一个input,该怎么办?这是一个SyntaxError,正等着发生。

递归会毁了你的栈

如果您刚刚了解了递归,则可能会想在get_non_negative_int中使用它,以便处理while循环。

def get_non_negative_int(prompt):
    try:
        value = int(input(prompt))
    except ValueError:
        print("Sorry, I didn't understand that.")
        return get_non_negative_int(prompt)

    if value < 0:
        print("Sorry, your response must not be negative.")
        return get_non_negative_int(prompt)
    else:
        return value

这似乎在大多数情况下都可以正常工作,但是如果用户输入无效数据的次数足够多,该脚本将以RuntimeError:超出最大递归深度终止。您可能会认为"没有傻瓜会连续犯1000个错误",但是您却低估了傻瓜的聪明才智!

回答2:

为什么要先做一个whileTrue,然后跳出这个循环,而您也可以只将需求放在while语句中,因为您想要的只是一旦年龄就停止了? / p>

age = None
while age is None:
    input_value = input("Please enter your age: ")
    try:
        # try and convert the string input to a number
        age = int(input_value)
    except ValueError:
        # tell the user off
        print("{input} is not a number, please enter a number only".format(input=input_value))
if age >= 18:
    print("You are able to vote in the United States!")
else:
    print("You are not able to vote in the United States.")

这将导致以下结果:

Please enter your age: *potato*
potato is not a number, please enter a number only
Please enter your age: *5*
You are not able to vote in the United States.

这将起作用,因为年龄永远不会有没有意义的值,并且代码遵循您的"业务流程"的逻辑

回答3:

尽管公认的答案是惊人的。我也想分享一个快速解决此问题的方法。 (这也解决了负面的年龄问题。)

f=lambda age: (age.isdigit() and ((int(age)>=18  and "Can vote" ) or "Cannot vote")) or \
f(input("invalid input. Try again\nPlease enter your age: "))
print(f(input("Please enter your age: ")))

P.S。这段代码适用于python 3.x。

回答4:

因此,我最近在搞些类似的事情,于是我想到了以下解决方案,该解决方案使用了一种获取垃圾输入的方式,甚至可以以任何逻辑方式对其进行检查。

read_single_keypress()礼貌 https://stackoverflow.com/a/6599441/4532996

def read_single_keypress() -> str:
    """Waits for a single keypress on stdin.
    -- from :: https://stackoverflow.com/a/6599441/4532996
    """

    import termios, fcntl, sys, os
    fd = sys.stdin.fileno()
    # save old state
    flags_save = fcntl.fcntl(fd, fcntl.F_GETFL)
    attrs_save = termios.tcgetattr(fd)
    # make raw - the way to do this comes from the termios(3) man page.
    attrs = list(attrs_save) # copy the stored version to update
    # iflag
    attrs[0] &= ~(termios.IGNBRK | termios.BRKINT | termios.PARMRK
                  | termios.ISTRIP | termios.INLCR | termios. IGNCR
                  | termios.ICRNL | termios.IXON )
    # oflag
    attrs[1] &= ~termios.OPOST
    # cflag
    attrs[2] &= ~(termios.CSIZE | termios. PARENB)
    attrs[2] |= termios.CS8
    # lflag
    attrs[3] &= ~(termios.ECHONL | termios.ECHO | termios.ICANON
                  | termios.ISIG | termios.IEXTEN)
    termios.tcsetattr(fd, termios.TCSANOW, attrs)
    # turn off non-blocking
    fcntl.fcntl(fd, fcntl.F_SETFL, flags_save & ~os.O_NONBLOCK)
    # read a single keystroke
    try:
        ret = sys.stdin.read(1) # returns a single character
    except KeyboardInterrupt:
        ret = 0
    finally:
        # restore old state
        termios.tcsetattr(fd, termios.TCSAFLUSH, attrs_save)
        fcntl.fcntl(fd, fcntl.F_SETFL, flags_save)
    return ret

def until_not_multi(chars) -> str:
    """read stdin until !(chars)"""
    import sys
    chars = list(chars)
    y = ""
    sys.stdout.flush()
    while True:
        i = read_single_keypress()
        _ = sys.stdout.write(i)
        sys.stdout.flush()
        if i not in chars:
            break
        y += i
    return y

def _can_you_vote() -> str:
    """a practical example:
    test if a user can vote based purely on keypresses"""
    print("can you vote? age : ", end="")
    x = int("0" + until_not_multi("0123456789"))
    if not x:
        print("\nsorry, age can only consist of digits.")
        return
    print("your age is", x, "\nYou can vote!" if x >= 18 else "Sorry! you can't vote")

_can_you_vote()

您可以在此处找到完整的模块。

示例:

$ ./input_constrain.py
can you vote? age : a
sorry, age can only consist of digits.
$ ./input_constrain.py 
can you vote? age : 23<RETURN>
your age is 23
You can vote!
$ _

请注意,此实现的性质是,一旦读取到不是数字的内容,它将关闭stdin。我没有在a之后按回车键,但是我需要在数字后面输入。

您可以将其与thismany()函数合并到同一模块中,以仅允许输入三位数。

回答5:

功能方法或" 看起来没有循环! ":

from itertools import chain, repeat

prompts = chain(["Enter a number: "], repeat("Not a number! Try again: "))
replies = map(input, prompts)
valid_response = next(filter(str.isdigit, replies))
print(valid_response)
Enter a number:  a
Not a number! Try again:  b
Not a number! Try again:  1
1

或者如果您想将"错误输入"消息与输入提示分开,如其他答案所示:

prompt_msg = "Enter a number: "
bad_input_msg = "Sorry, I didn't understand that."
prompts = chain([prompt_msg], repeat('\n'.join([bad_input_msg, prompt_msg])))
replies = map(input, prompts)
valid_response = next(filter(str.isdigit, replies))
print(valid_response)
Enter a number:  a
Sorry, I didn't understand that.
Enter a number:  b
Sorry, I didn't understand that.
Enter a number:  1
1

它如何工作?

  1. prompts = chain(["Enter a number: "], repeat("Not a number! Try again: "))
    
    itertools.chain的组合 itertools.repeat 将创建一个迭代器,该迭代器将生成字符串"输入数字:"一次,而"不是数字!请重试:"无限次:
    for prompt in prompts:
        print(prompt)
    
    Enter a number: 
    Not a number! Try again: 
    Not a number! Try again: 
    Not a number! Try again: 
    # ... and so on
    
  2. replies=map(输入,提示)-此处 map 会将上一步中的所有提示字符串应用于 input 函数。例如:
    for reply in replies:
        print(reply)
    
    Enter a number:  a
    a
    Not a number! Try again:  1
    1
    Not a number! Try again:  it doesn't care now
    it doesn't care now
    # and so on...
    
  3. 我们使用 filter str.isdigit 来过滤出仅包含那些字符串数字:
    only_digits = filter(str.isdigit, replies)
    for reply in only_digits:
        print(reply)
    
    Enter a number:  a
    Not a number! Try again:  1
    1
    Not a number! Try again:  2
    2
    Not a number! Try again:  b
    Not a number! Try again: # and so on...
    
    为了只获取第一个数字字符串,我们使用 下一个

其他验证规则:

  1. 字符串方法:当然,您可以使用其他字符串方法,例如 str.isalpha 仅获取字母字符串,或 str.isupper 仅获取大写字母。有关完整列表,请参见文档

  2. 成员资格测试:
    有几种不同的执行方法。其中之一是使用 __contains__ 方法:

    from itertools import chain, repeat
    
    fruits = {'apple', 'orange', 'peach'}
    prompts = chain(["Enter a fruit: "], repeat("I don't know this one! Try again: "))
    replies = map(input, prompts)
    valid_response = next(filter(fruits.__contains__, replies))
    print(valid_response)
    
    Enter a fruit:  1
    I don't know this one! Try again:  foo
    I don't know this one! Try again:  apple
    apple
    
  3. 数字比较:
    这里有一些有用的比较方法。例如,对于 __lt__ (< > <):

    from itertools import chain, repeat
    
    prompts = chain(["Enter a positive number:"], repeat("I need a positive number! Try again:"))
    replies = map(input, prompts)
    numeric_strings = filter(str.isnumeric, replies)
    numbers = map(float, numeric_strings)
    is_positive = (0.).__lt__
    valid_response = next(filter(is_positive, numbers))
    print(valid_response)
    
    Enter a positive number: a
    I need a positive number! Try again: -5
    I need a positive number! Try again: 0
    I need a positive number! Try again: 5
    5.0
    

    或者,如果您不喜欢使用dunder方法(dunder =双下划线),则可以始终定义自己的函数,或使用 operator 模块。

  4. 路径存在:
    这里可以使用pathlib库及其
    Path.exists 方法:

    from itertools import chain, repeat
    from pathlib import Path
    
    prompts = chain(["Enter a path: "], repeat("This path doesn't exist! Try again: "))
    replies = map(input, prompts)
    paths = map(Path, replies)
    valid_response = next(filter(Path.exists, paths))
    print(valid_response)
    
    Enter a path:  a b c
    This path doesn't exist! Try again:  1
    This path doesn't exist! Try again:  existing_file.txt
    existing_file.txt
    

尝试次数上限:

如果您不想无限次折磨用户,可以在 itertools.repeat 。这可以与为 next 提供默认值结合使用a>函数:

from itertools import chain, repeat

prompts = chain(["Enter a number:"], repeat("Not a number! Try again:", 2))
replies = map(input, prompts)
valid_response = next(filter(str.isdigit, replies), None)
print("You've failed miserably!" if valid_response is None else 'Well done!')
Enter a number: a
Not a number! Try again: b
Not a number! Try again: c
You've failed miserably!

预处理输入数据:

有时候,如果用户不小心输入了 IN CAPS 或在字符串的开头或结尾都带有空格,我们就不想拒绝输入。要考虑这些简单的错误,我们可以通过应用 str来预处理输入数据.lower str.strip 方法。例如,对于成员资格测试,代码如下所示:

from itertools import chain, repeat

fruits = {'apple', 'orange', 'peach'}
prompts = chain(["Enter a fruit: "], repeat("I don't know this one! Try again: "))
replies = map(input, prompts)
lowercased_replies = map(str.lower, replies)
stripped_replies = map(str.strip, lowercased_replies)
valid_response = next(filter(fruits.__contains__, stripped_replies))
print(valid_response)
Enter a fruit:  duck
I don't know this one! Try again:     Orange
orange

如果要使用许多函数进行预处理,则使用执行功能组成。例如,使用此处中的一个:

from itertools import chain, repeat

from lz.functional import compose

fruits = {'apple', 'orange', 'peach'}
prompts = chain(["Enter a fruit: "], repeat("I don't know this one! Try again: "))
replies = map(input, prompts)
process = compose(str.strip, str.lower)  # you can add more functions here
processed_replies = map(process, replies)
valid_response = next(filter(fruits.__contains__, processed_replies))
print(valid_response)
Enter a fruit:  potato
I don't know this one! Try again:   PEACH
peach

合并验证规则:

例如,在一个简单的情况下,当程序要求输入1到120岁之间的年龄时,只需添加另一个filter

from itertools import chain, repeat

prompt_msg = "Enter your age (1-120): "
bad_input_msg = "Wrong input."
prompts = chain([prompt_msg], repeat('\n'.join([bad_input_msg, prompt_msg])))
replies = map(input, prompts)
numeric_replies = filter(str.isdigit, replies)
ages = map(int, numeric_replies)
positive_ages = filter((0).__lt__, ages)
not_too_big_ages = filter((120).__ge__, positive_ages)
valid_response = next(not_too_big_ages)
print(valid_response)

但是在有很多规则的情况下,最好实现执行逻辑合取。在下面的示例中,我将使用此处

from functools import partial
from itertools import chain, repeat

from lz.logical import conjoin


def is_one_letter(string: str) -> bool:
    return len(string) == 1


rules = [str.isalpha, str.isupper, is_one_letter, 'C'.__le__, 'P'.__ge__]

prompt_msg = "Enter a letter (C-P): "
bad_input_msg = "Wrong input."
prompts = chain([prompt_msg], repeat('\n'.join([bad_input_msg, prompt_msg])))
replies = map(input, prompts)
valid_response = next(filter(conjoin(*rules), replies))
print(valid_response)
Enter a letter (C-P):  5
Wrong input.
Enter a letter (C-P):  f
Wrong input.
Enter a letter (C-P):  CDE
Wrong input.
Enter a letter (C-P):  Q
Wrong input.
Enter a letter (C-P):  N
N

不幸的是,如果有人为每个失败的案例需要自定义消息,那么恐怕就没有 pretty 功能。或者,至少我找不到一个。

回答6:

使用 点击

Click 是用于命令行界面的库,它提供了向用户询问有效响应的功能。

简单的例子:

import click

number = click.prompt('Please enter a number', type=float)
print(number)
Please enter a number: 
 a
Error: a is not a valid floating point value
Please enter a number: 
 10
10.0

请注意如何将字符串值自动转换为浮点数。

检查值是否在范围内:

提供了不同的自定义类型。要获得特定范围内的数字,我们可以使用IntRange

age = click.prompt("What's your age?", type=click.IntRange(1, 120))
print(age)
What's your age?: 
 a
Error: a is not a valid integer
What's your age?: 
 0
Error: 0 is not in the valid range of 1 to 120.
What's your age?: 
 5
5

我们还可以仅指定一个限制,minmax

age = click.prompt("What's your age?", type=click.IntRange(min=14))
print(age)
What's your age?: 
 0
Error: 0 is smaller than the minimum valid value 14.
What's your age?: 
 18
18

会员资格测试:

使用click.Choice类型。默认情况下,此检查区分大小写。

choices = {'apple', 'orange', 'peach'}
choice = click.prompt('Provide a fruit', type=click.Choice(choices, case_sensitive=False))
print(choice)
Provide a fruit (apple, peach, orange): 
 banana
Error: invalid choice: banana. (choose from apple, peach, orange)
Provide a fruit (apple, peach, orange): 
 OrAnGe
orange

使用路径和文件:

使用click.Path类型,我们可以检查现有路径并解决它们:

path = click.prompt('Provide path', type=click.Path(exists=True, resolve_path=True))
print(path)
Provide path: 
 nonexistent
Error: Path "nonexistent" does not exist.
Provide path: 
 existing_folder
'/path/to/existing_folder

可以通过click.File

来读写文件。
file = click.prompt('In which file to write data?', type=click.File('w'))
with file.open():
    file.write('Hello!')
# More info about `lazy=True` at:
# https://click.palletsprojects.com/en/7.x/arguments/#file-opening-safety
file = click.prompt('Which file you wanna read?', type=click.File(lazy=True))
with file.open():
    print(file.read())
In which file to write data?: 
         # <-- provided an empty string, which is an illegal name for a file
In which file to write data?: 
 some_file.txt
Which file you wanna read?: 
 nonexistent.txt
Error: Could not open file: nonexistent.txt: No such file or directory
Which file you wanna read?: 
 some_file.txt
Hello!

其他示例:

密码确认:

password = click.prompt('Enter password', hide_input=True, confirmation_prompt=True)
print(password)
Enter password: 
 ······
Repeat for confirmation: 
 ·
Error: the two entered values do not match
Enter password: 
 ······
Repeat for confirmation: 
 ······
qwerty

默认值:

在这种情况下,只需按 Enter (或您使用的任何键)而不输入值,即可得到默认值:

number = click.prompt('Please enter a number', type=int, default=42)
print(number)
Please enter a number [42]: 
 a
Error: a is not a valid integer
Please enter a number [42]: 

42

回答7:

def validate_age(age):
    if age >=0 :
        return True
    return False

while True:
    try:
        age = int(raw_input("Please enter your age:"))
        if validate_age(age): break
    except ValueError:
        print "Error: Invalid age."

回答8:

在Daniel Q和Patrick Artner的出色建议的基础上,这是一个更为通用的解决方案。

# Assuming Python3
import sys

class ValidationError(ValueError):  # thanks Patrick Artner
    pass

def validate_input(prompt, cast=str, cond=(lambda x: True), onerror=None):
    if onerror==None: onerror = {}
    while True:
        try:
            data = cast(input(prompt))
            if not cond(data): raise ValidationError
            return data
        except tuple(onerror.keys()) as e:  # thanks Daniel Q
            print(onerror[type(e)], file=sys.stderr)

我选择了显式的ifraise语句,而不是assert,因为可以关闭断言检查,而应该始终进行验证可以提供强大的功能。

这可以用于获取具有不同验证条件的不同种类的输入。例如:

# No validation, equivalent to simple input:
anystr = validate_input("Enter any string: ")

# Get a string containing only letters:
letters = validate_input("Enter letters: ",
    cond=str.isalpha,
    onerror={ValidationError: "Only letters, please!"})

# Get a float in [0, 100]:
percentage = validate_input("Percentage? ",
    cast=float, cond=lambda x: 0.0<=x<=100.0,
    onerror={ValidationError: "Must be between 0 and 100!",
             ValueError: "Not a number!"})

或者,回答原始问题:

age = validate_input("Please enter your age: ",
        cast=int, cond=lambda a:0<=a<150,
        onerror={ValidationError: "Enter a plausible age, please!",
                 ValueError: "Enter an integer, please!"})
if age >= 18: 
    print("You are able to vote in the United States!")
else:
    print("You are not able to vote in the United States.")

回答9:

试试这个:-

def takeInput(required):
  print 'ooo or OOO to exit'
  ans = raw_input('Enter: ')

  if not ans:
      print "You entered nothing...!"
      return takeInput(required) 

      ##  FOR Exit  ## 
  elif ans in ['ooo', 'OOO']:
    print "Closing instance."
    exit()

  else:
    if ans.isdigit():
      current = 'int'
    elif set('[~!@#$%^&*()_+{}":/\']+$').intersection(ans):
      current = 'other'
    elif isinstance(ans,basestring):
      current = 'str'        
    else:
      current = 'none'

  if required == current :
    return ans
  else:
    return takeInput(required)

## pass the value in which type you want [str/int/special character(as other )]
print "input: ", takeInput('str')

回答10:

虽然try / except块将起作用,但是完成此任务的更快,更干净的方法是使用str.isdigit()。

while True:
    age = input("Please enter your age: ")
    if age.isdigit():
        age = int(age)
        break
    else:
        print("Invalid number '{age}'. Try again.".format(age=age))

if age >= 18: 
    print("You are able to vote in the United States!")
else:
    print("You are not able to vote in the United States.")

回答11:

使用自定义的ValidationError和用于整数输入的(可选)范围验证的输入验证的另一种解决方案:

class ValidationError(ValueError): 
    """Special validation error - its message is supposed to be printed"""
    pass

def RangeValidator(text,num,r):
    """Generic validator - raises 'text' as ValidationError if 'num' not in range 'r'."""
    if num in r:
        return num
    raise ValidationError(text)

def ValidCol(c): 
    """Specialized column validator providing text and range."""
    return RangeValidator("Columns must be in the range of 0 to 3 (inclusive)", 
                          c, range(4))

def ValidRow(r): 
    """Specialized row validator providing text and range."""
    return RangeValidator("Rows must be in the range of 5 to 15(exclusive)",
                          r, range(5,15))

用法:

def GetInt(text, validator=None):
    """Aks user for integer input until a valid integer is given. If provided, 
    a 'validator' function takes the integer and either raises a 
    ValidationError to be printed or returns the valid number. 
    Non integers display a simple error message."""
    print()
    while True:
        n = input(text)
        try:
            n = int(n)

            return n if validator is None else validator(n)

        except ValueError as ve:
            # prints ValidationErrors directly - else generic message:
            if isinstance(ve, ValidationError):
                print(ve)
            else:
                print("Invalid input: ", n)


column = GetInt("Pleased enter column: ", ValidCol)
row = GetInt("Pleased enter row: ", ValidRow)
print( row, column)

输出:

Pleased enter column: 22
Columns must be in the range of 0 to 3 (inclusive)
Pleased enter column: -2
Columns must be in the range of 0 to 3 (inclusive)
Pleased enter column: 2
Pleased enter row: a
Invalid input:  a
Pleased enter row: 72
Rows must be in the range of 5 to 15(exclusive)
Pleased enter row: 9  

9, 2

回答12:

好问题!您可以尝试以下代码。 =)

此代码使用 ast.literal_eval()查找输入的数据类型(age)。然后遵循以下算法:

  1. 要求用户输入他/他的年龄

    1.1。如果agefloatint数据类型:

    • 检查是否age>=18。如果age>=18,则打印适当的输出并退出。

    • 检查是否0 <18 。如果0 <18 ,则打印适当的输出并退出。

    • 如果age<=0,请要求用户再次输入有效的年龄编号,( ie 返回步骤1。)

    1.2。如果age不是floatint数据类型,则要求用户再次输入其年龄( ie 返回步骤1。)

这是代码。

from ast import literal_eval

''' This function is used to identify the data type of input data.'''
def input_type(input_data):
    try:
        return type(literal_eval(input_data))
    except (ValueError, SyntaxError):
        return str

flag = True

while(flag):
    age = raw_input("Please enter your age: ")

    if input_type(age)==float or input_type(age)==int:
        if eval(age)>=18: 
            print("You are able to vote in the United States!") 
            flag = False 
        elif eval(age)>0 and eval(age)<18: 
            print("You are not able to vote in the United States.") 
            flag = False
        else: print("Please enter a valid number as your age.")

    else: print("Sorry, I didn't understand that.") 

回答13:

使用递归功能的持久用户输入:

字符串

def askName():
    return input("Write your name: ").strip() or askName()

name = askName()

整数

def askAge():
    try: return int(input("Enter your age: "))
    except ValueError: return askAge()

age = askAge()

最后,问题要求:

def askAge():
    try: return int(input("Enter your age: "))
    except ValueError: return askAge()

age = askAge()

responseAge = [
    "You are able to vote in the United States!",
    "You are not able to vote in the United States.",
][int(age < 18)]

print(responseAge)

回答14:

您始终可以应用简单的if-else逻辑,并在代码中添加一个if逻辑以及for循环。

while True:
     age = int(input("Please enter your age: "))
     if (age >= 18)  : 
         print("You are able to vote in the United States!")
     if (age < 18) & (age > 0):
         print("You are not able to vote in the United States.")
     else:
         print("Wrong characters, the input must be numeric")
         continue

这将是一个无限次的厕所,您将被要求无限期地输入年龄。

回答15:

您可以编写更通用的逻辑,以允许用户仅输入特定的次数,因为在许多实际应用程序中会出现相同的用例。

def getValidInt(iMaxAttemps = None):
  iCount = 0
  while True:
    # exit when maximum attempt limit has expired
    if iCount != None and iCount > iMaxAttemps:
       return 0     # return as default value

    i = raw_input("Enter no")
    try:
       i = int(i)
    except ValueError as e:
       print "Enter valid int value"
    else:
       break

    return i

age = getValidInt()
# do whatever you want to do.

回答16:

您可以将输入语句设置为True循环,以便它反复询问用户输入,然后在用户输入您想要的响应时中断该循环。而且,您可以使用try和except块来处理无效响应。

while True:

    var = True

    try:
        age = int(input("Please enter your age: "))

    except ValueError:
        print("Invalid input.")
        var = False

    if var == True:
        if age >= 18:
                print("You are able to vote in the United States.")
                break
        else:
            print("You are not able to vote in the United States.")

var变量就是这样,如果用户输入一个字符串而不是一个整数,程序将不会返回"您无法在美国投票"。

回答17:

使用" while"语句,直到用户输入一个真值,并且如果输入值不是数字或它是空值,请跳过该语句并尝试再次询问,依此类推。例如,我试图真正回答您的问题。如果我们认为年龄在1到150之间,则接受输入值,否则输入的值是错误的。对于终止程序,用户可以使用0键并将其作为值输入。

注意:请阅读代码顶部的注释。

# If your input value is only a number then use "Value.isdigit() == False".
# If you need an input that is a text, you should remove "Value.isdigit() == False".
def Input(Message):
    Value = None
    while Value == None or Value.isdigit() == False:
        try:        
            Value = str(input(Message)).strip()
        except InputError:
            Value = None
    return Value

# Example:
age = 0
# If we suppose that our age is between 1 and 150 then input value accepted,
# else it's a wrong value.
while age <=0 or age >150:
    age = int(Input("Please enter your age: "))
    # For terminating program, the user can use 0 key and enter it as an a value.
    if age == 0:
        print("Terminating ...")
        exit(0)

if age >= 18 and age <=150: 
    print("You are able to vote in the United States!")
else:
    print("You are not able to vote in the United States.")

回答18:

这是一个更简洁,更通用的解决方案,避免了重复的if / else块:编写一个在字典中使用(错误,错误提示)对的函数,并使用断言进行所有值检查。

def validate_input(prompt, error_map):
    while True:
        try:
            data = int(input(prompt))
            # Insert your non-exception-throwing conditionals here
            assert data > 0
            return data
        # Print whatever text you want the user to see
        # depending on how they messed up
        except tuple(error_map.keys()) as e:
            print(error_map[type(e)])

用法:

d = {ValueError: 'Integers only', AssertionError: 'Positive numbers only', 
     KeyboardInterrupt: 'You can never leave'}
user_input = validate_input("Positive number: ", d)

回答19:

简单的解决方案是:

while True:
    age = int(input("Please enter your age: "))

    if (age<=0) or (age>120):
        print('Sorry, I did not understand that.Please try again')
        continue
    else:

        if age>=18:
            print("You are able to vote in the United States!")
        else:
            print("You are not able to vote in the United States.")
        break

上面的代码说明:为了使年龄有效,该年龄应该为正,并且不得超过正常的身体年龄,例如,最大年龄为120。

然后我们可以询问用户年龄,如果年龄输入为负数或大于120,我们认为该输入无效,然后要求用户重试。

输入有效输入后,我们将执行检查(使用嵌套的if-else语句),确定年龄是否大于等于18,反之亦然,并显示一条消息,说明用户是否有资格投票

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