input_utils.py

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