APT command line interface-like yes no input

Question

Is there any short way to achieve what the APT  Advanced Package Tool  command line interface does in Python   I mean  when the package manager prompts a yes no question followed by  Yes no   the script accepts YES Y yes y or Enter  defaults to Yes as hinted by the capital letter    The only thing I find in the official docs is input and raw input     I know it s not that hard to emulate  but it s annoying to rewrite

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As a programming noob  I found a bunch of the above answers overly complex  especially if the goal is to have a simple function that you can pass various yes no questions to  forcing the user to select yes or no  After scouring this page and several others  and borrowing all of the various good ideas  I ended up with the following   def yes no question to be answered       while True          choice   input question to be answered  lower           if choice  1      y                return True         elif choice  1      n               return False         else              print  Please respond with  Yes  or  No  n     See it in Practice below   musical taste   yes no  Do you like Pine Coladas    if musical taste    True      print  and getting caught in the rain   elif musical taste    False      print  You clearly have no taste in music

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For Python 3  I m using this function  def user prompt question  str  - gt  bool       quot  quot  quot  Prompt the yes no- question  to the user   quot  quot  quot      from distutils util import strtobool      while True          user input   input question    quot   y n    quot           try              return bool strtobool user input           except ValueError              print  quot Please use y n or yes no  n quot    The strtobool   function converts a string into a bool  If the string cant be parsed it will raise a ValueError  In Python 3 raw input   has been renamed to input    As Geoff said  strtobool actually returns 0 or 1  therefore the result has to be cast to bool   This is the implementation of strtobool  if you want special words to be recognized as true  you can copy the code and add your own cases  def strtobool  val        quot  quot  quot Convert a string representation of truth to true  1  or false  0       True values are  y    yes    t    true    on   and  1   false values     are  n    no    f    false    off   and  0    Raises ValueError if      val  is anything else       quot  quot  quot      val   val lower       if val in   y    yes    t    true    on    1            return 1     elif val in   n    no    f    false    off    0            return 0     else          raise ValueError  quot invalid truth value  r quot     val

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You can use click s confirm method   import click  if click confirm  Do you want to continue    default True       print  Do something     This will print     Do you want to continue   Y n     Should work for Python 2 3 on Linux  Mac or Windows   Docs  http   click pocoo org 5 prompts  confirmation-prompts

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I modified fmark s answer to by python 2 3 compatible more pythonic   See ipython s utility module if you are interested in something with more error handling    PY2 3 compatibility from   future   import print function   You could use the six package for this try      input    raw input except NameError      input    input  def query yes no question  default True          Ask a yes no question via standard input and return the answer       If invalid input is given  the user will be asked until     they acutally give valid input       Args          question str               A question that is presented to the user          default bool None               The default value when enter is pressed with no value              When None  there is no default value and the query             will loop      Returns          A bool indicating whether user has entered yes or no       Side Effects          Blocks program execution until valid input y n  is given              yes list     yes    y       no list     no    n        default dict        default   gt  prompt default string         None    y n            True    Y n            False    y N               default str   default dict default      prompt str     s  s      question  default str       while True          choice   input  prompt str  lower            if not choice and default is not None              return default         if choice in yes list              return True         if choice in no list              return False          notification str    Please respond with  y  or  n           print notification str

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This is what I use   import sys    cs   case sensitive   ys   whatever you want to be  yes  - string or tuple of strings     prompt  promptString      1                  only y    prompt  promptString  cs   0     1           y or Y    prompt  promptString   Yes      1            only Yes    prompt  promptString    y   yes       1      only y or yes    prompt  promptString    Y   Yes       1      only Y or Yes    prompt  promptString    y   yes   0     1    Yes  YES  yes  y  Y etc   def prompt ps ys  y  cs 1       sys stdout write ps      ii   raw input       if cs    0          ii   ii lower       if type ys     tuple          for accept in ys              if cs    0                  accept   accept lower               if ii    accept                  return True     else          if ii    ys              return True     return False

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A very simple  but not very sophisticated  way of doing this for a single choice would be   msg    Shall I   shall   input   s  y N      msg  lower       y    You could also write a simple  slightly improved  function around this   def yn choice message  default  y        choices    Y n  if default lower   in   y    yes   else  y N      choice   input   s   s       message  choices       values     y    yes       if choices     Y n  else   y    yes       return choice strip   lower   in values   Note  On Python 2  use raw input instead of input

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There is a function strtobool in Python s standard library  http   docs python org 2 distutils apiref html highlight distutils util distutils util strtobool  You can use it to check user s input and transform it to True or False value

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Here s my take on it  I simply wanted to abort if the user did not affirm the action   import distutils  if unsafe case      print  Proceed with potentially unsafe thing   y n        while True          try              verify   distutils util strtobool raw input                if not verify                  raise SystemExit    Abort on user reject             break         except ValueError as err              print  Please enter   yes   or   no                   Try again     print  Continuing       do unsafe thing

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I know this has been answered a bunch of ways and this may not answer OP s specific question  with the list of criteria  but this is what I did for the most common use case and it s far simpler than the other responses   answer   input  Please indicate approval   y n    if not answer or answer 0  lower       y       print  You did not indicate approval       exit 1

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A cleaned up Python 3 example     inputExample py  def confirm input question  default  no           Ask a yes no question and return their answer        question  is a string that is presented to the user       default  is the presumed answer if the user just hits  lt Enter gt           It must be  yes    no   or None  meaning         an answer is required of the user        The  answer  return value is True for  yes  or False for  no               valid     yes   True   y   True   ye   True                no   False   n   False      if default is None          prompt      y n        elif default     yes           prompt      Y n        elif default     no           prompt      y N        else          raise ValueError  invalid default answer         format default        while True          print question   prompt          choice   input   lower           if default is not None and choice                    return valid default          elif choice in valid              return valid choice          else              print  Please respond with  yes  or  no                                   or  y  or  n    n    def main         if confirm input   nDo you want to continue              print  You said yes because the function equals true  Continuing        else          print  Quitting because the function equals false     if   name         main         main

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One-liner with Python 3 8 and above  while res   input  quot When correct  press enter to continue    quot   lower   not in   y   yes   Y   YES       pass

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As you mentioned  the easiest way is to use raw input    or simply input   for Python 3   There is no built-in way to do this  From Recipe 577058   import sys  def query yes no question  default  yes           Ask a yes no question via raw input   and return their answer        question  is a string that is presented to the user       default  is the presumed answer if the user just hits  lt Enter gt           It must be  yes   the default    no  or None  meaning         an answer is required of the user        The  answer  return value is True for  yes  or False for  no               valid     yes   True   y   True   ye   True                no   False   n   False      if default is None          prompt      y n        elif default     yes           prompt      Y n        elif default     no           prompt      y N        else          raise ValueError  invalid default answer    s     default       while True          sys stdout write question   prompt          choice   raw input   lower           if default is not None and choice                    return valid default          elif choice in valid              return valid choice          else              sys stdout write  Please respond with  yes  or  no                                   or  y  or  n    n     Usage example    gt  gt  gt  query yes no  Is cabbage yummier than cauliflower    Is cabbage yummier than cauliflower   Y n  oops Please respond with  yes  or  no   or  y  or  n    Is cabbage yummier than cauliflower   Y n   ENTER   gt  gt  gt  True   gt  gt  gt  query yes no  Is cabbage yummier than cauliflower    None  Is cabbage yummier than cauliflower   y n   ENTER  Please respond with  yes  or  no   or  y  or  n    Is cabbage yummier than cauliflower   y n  y  gt  gt  gt  True

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Doing the same with python 3 x  where raw input   doesn t exist   def ask question  default   None       hasDefault   default is not None     prompt    question                            y    Y   hasDefault and default                            n    N   hasDefault and not default               while True          sys stdout write prompt          choice   input   strip   lower           if choice                    if default is not None                  return default         else              if  yes  startswith choice                   return True             if  no  startswith choice                   return False          sys stdout write  Please respond with  yes  or  no                                   or  y  or  n    n

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as mentioned by  Alexander Artemenko  here s a simple solution using strtobool  from distutils util import strtobool  def user yes no query question       sys stdout write   s  y n  n    question      while True          try              return strtobool raw input   lower            except ValueError              sys stdout write  Please respond with   y   or   n    n     usage   gt  gt  gt  user yes no query  Do you like cheese    Do you like cheese   y n  Only on tuesdays Please respond with  y  or  n   ok Please respond with  y  or  n   y  gt  gt  gt  True

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You can also use prompter   Shamelessly taken from the README    pip install prompter  from prompter import yesno   gt  gt  gt  yesno  Really    Really   Y n  True   gt  gt  gt  yesno  Really    Really   Y n  no False   gt  gt  gt  yesno  Really    default  no   Really   y N  True

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How about this    def yes prompt    Please enter Yes No      while True      try          i   raw input prompt      except KeyboardInterrupt          return False     if i lower   in   yes   y    return True     elif i lower   in   no   n    return False

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def question question  answers       acceptable   False     while not acceptable          print question    specify   s  or   s      answers         answer   raw input           if answer lower      answers 0  lower   or answers 0  lower                print  Answer     s     answer             acceptable   True     return answer  raining   question  Is it raining today      Y    N      This is how I d do it   Output  Is it raining today  Specify  Y  or  N   gt  Y answer    Y

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on 2 7  is this too non-pythonic   if raw input  your prompt   lower   0    y      your code here else     alternate code here   it captures any variation of Yes at least

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Python x x res   True while res      res   input  quot Please confirm with y yes    quot   lower    res   res not in   y   yes   Y   YES

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I d do it this way     raw input returns the empty string for  enter  yes     yes   y    ye       no     no   n    choice   raw input   lower   if choice in yes     return True elif choice in no     return False else     sys stdout write  Please respond with  yes  or  no

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Since the answer is expected yes or no  in the examples below  the first solution is to repeat the question using the function while  and the second solution is to use recursion - is the process of defining something in terms of itself  def yes or no question       while  quot the answer is invalid quot           reply   str input question    y n       lower   strip           if reply  1      y               return True         if reply  1      n               return False  yes or no  quot Do you know who Novak Djokovic is  quot    second solution  def yes or no question        quot  quot  quot Simple Yes No Function  quot  quot  quot      prompt   f  question     y n         answer   input prompt  strip   lower       if answer not in   y    n            print f  answer  is invalid  please try again              return yes or no question      if answer     y           return True     return False  def main         quot  quot  quot Run main function  quot  quot  quot      answer   yes or no  quot Do you know who Novak Djokovic is  quot       print f you answer was   answer      if   name         main         main

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You could try something like the code below to be able to work with choices from the variable  accepted  show here   print   accepted      format accepted      accepted    yes         Yes    yes    YES    y    Y     no     No    no    NO    n    N      Here is the code        usr bin python3  def makeChoi yeh  neh       accept            for w in words      accept  yes           yeh  yeh lower    yeh upper    yeh lower   0   yeh upper   0        accept  no       neh  neh lower    neh upper    neh lower   0   neh upper   0        return accept  accepted   makeChoi  Yes    No    def doYeh        print  Yeh  Let  s do it     def doNeh        print  Neh  Let  s not do it     choi   None while not choi      choi   input   Please choose  Y n          if choi in accepted  yes            choi   True         doYeh       elif choi in accepted  no            choi   True         doNeh       else          print  Your choice was       Please use an accepted input value     format choi           print  accepted           choi   None

[python] APT command line interface-like yes/no input?

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