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Contains our Question class, which knows how to ask a question, then
run abitrary code.
Copyright 2019 Canonical Ltd
Licensed under the Apache License, Version 2.0 (the "License");
you may not use this file except in compliance with the License.
You may obtain a copy of the License at
Unless required by applicable law or agreed to in writing, software
distributed under the License is distributed on an "AS IS" BASIS,
See the License for the specific language governing permissions and
limitations under the License.
from typing import Tuple
class InvalidQuestion(Exception):
"""Exception to raies in the case where a Question subclass has not
been properly implemented.
class InvalidAnswer(Exception):
"""Exception to raise in the case where the user has specified an
invalid answer.
class AnswerNotImplemented(Exception):
"""Exception to raise in the case where a 'yes' or 'no' routine has
not been overriden in the subclass, as required.
class Question():
Ask the user a question, and then run code as appropriate.
Contains a support for always defaulting to yes.
TODO: Add support for finding answers in a config.yaml.
_valid_types = [
'binary', # Yes or No, and variants thereof
'string', # Accept (and sanitize) any string
'auto' # Don't actually ask a question -- just execute self.yes(True)
_question = '(required)'
_type = 'auto' # can be binary, string or auto
_invalid_prompt = 'Please answer Yes or No.'
_retries = 3
_input_func = input
def __init__(self):
if self._type not in ['binary', 'string', 'auto']:
raise InvalidQuestion(
'Invalid type {} specified'.format(self._type))
def _validate(self, answer: bytes) -> Tuple[str, bool]:
"""Validate an answer.
:param anwser: raw input from the user.
Returns the answer, and whether or not the answer was valid.
if self._type == 'auto':
return True, True
answer = answer.decode('utf8')
if self._type == 'string':
# TODO Santize this!
return answer, True
# self._type is binary
if answer.lower() in ['y', 'yes']:
return True, True
if answer.lower() in ['n', 'no']:
return False, True
return answer, False
def yes(self, answer: str) -> None:
"""Routine to run if the user answers 'yes' or with a value."""
raise AnswerNotImplemented('You must override this method.')
def no(self, answer: str) -> None:
"""Routine to run if the user answers 'no'"""
raise AnswerNotImplemented('You must override this method.')
def ask(self) -> None:
Ask the user a question.
Run self.yes or as appropriate. Raise an error if the
user cannot specify a valid answer after self._retries tries.
prompt = self._question
for i in range(0, self._retries):
awr, valid = self._validate(
self._type == 'auto' or self._input_func(prompt))
if valid:
if awr:
return self.yes(awr)
prompt = '{} is not valid. {}'.format(awr, self._invalid_prompt)
raise InvalidAnswer('Too many invalid answers.')