input_utils.py

   1 #!/usr/bin/env python3
   2
   3 """Utilities related to user input."""
   4
   5 import logging
   6 import signal
   7 import sys
   8 from typing import List
   9
  10 import readchar  # type: ignore
  11
  12 import exceptions
  13
  14 logger = logging.getLogger(__file__)
  15
  16
  17 def single_keystroke_response(
  18     valid_responses: List[str],
  19     *,
  20     prompt: str = None,
  21     default_response: str = None,
  22     timeout_seconds: int = None,
  23 ) -> str:
  24     """Get a single keystroke response to a prompt."""
  25
  26     def _handle_timeout(signum, frame) -> None:
  27         raise exceptions.TimeoutError()
  28
  29     def _single_keystroke_response_internal(
  30         valid_responses: List[str], timeout_seconds=None
  31     ) -> str:
  32         os_special_keystrokes = [3, 26]  # ^C, ^Z
  33         if timeout_seconds is not None:
  34             signal.signal(signal.SIGALRM, _handle_timeout)
  35             signal.alarm(timeout_seconds)
  36
  37         try:
  38             while True:
  39                 response = readchar.readchar()
  40                 logger.debug(f'Keystroke: {ord(response)}')
  41                 if response in valid_responses:
  42                     break
  43                 if ord(response) in os_special_keystrokes:
  44                     break
  45             return response
  46         finally:
  47             if timeout_seconds is not None:
  48                 signal.alarm(0)
  49
  50     if prompt is not None:
  51         print(prompt, end="")
  52         sys.stdout.flush()
  53     try:
  54         response = _single_keystroke_response_internal(valid_responses, timeout_seconds)
  55         if ord(response) == 3:
  56             raise KeyboardInterrupt('User pressed ^C in input_utils.')
  57
  58     except exceptions.TimeoutError:
  59         if default_response is not None:
  60             response = default_response
  61     if prompt is not None:
  62         print(response)
  63     return response
  64
  65
  66 def yn_response(prompt: str = None, *, timeout_seconds=None) -> str:
  67     """Get a Y/N response to a prompt."""
  68
  69     return single_keystroke_response(
  70         ["y", "n", "Y", "N"], prompt=prompt, timeout_seconds=timeout_seconds
  71     ).lower()
  72
  73
  74 def keystroke_helper() -> None:
  75     """Misc util to watch keystrokes and report what they were."""
  76
  77     print("Watching for keystrokes; ^C to quit.")
  78     while True:
  79         key = readchar.readkey()
  80         if len(key) == 1:
  81             print(f'That was "{key}" ({ord(key)}).')
  82             if ord(key) == 3:
  83                 return
  84         else:
  85             print(f'That was sequence "{key}" (', end="")
  86             for _ in key:
  87                 print(f" {ord(_)} ", end="")
  88             print(")")