Reset the terminal without clearing it.

reset_tty.py

#!/usr/bin/env python3
# vim: set fdm=marker:

# Copyright (c) 2024 S. Zeid.
# 
# Permission to use, copy, modify, and/or distribute this software for any
# purpose with or without fee is hereby granted.
# 
# THE SOFTWARE IS PROVIDED "AS IS" AND THE AUTHOR DISCLAIMS ALL WARRANTIES
# WITH REGARD TO THIS SOFTWARE INCLUDING ALL IMPLIED WARRANTIES OF
# MERCHANTABILITY AND FITNESS. IN NO EVENT SHALL THE AUTHOR BE LIABLE FOR
# ANY SPECIAL, DIRECT, INDIRECT, OR CONSEQUENTIAL DAMAGES OR ANY DAMAGES
# WHATSOEVER RESULTING FROM LOSS OF USE, DATA OR PROFITS, WHETHER IN AN
# ACTION OF CONTRACT, NEGLIGENCE OR OTHER TORTIOUS ACTION, ARISING OUT OF
# OR IN CONNECTION WITH THE USE OR PERFORMANCE OF THIS SOFTWARE.

"""Reset the terminal without clearing it.

A file descriptor may be given as an argument.  If omitted, it defaults
to standard output.

Does nothing if the given file descriptor is not a TTY, or if the platform
is unsupported.

"""


def main(argv: list[str]) -> int:  #{{{1
  if len(argv) > 1:
    reset_tty(int(argv[1]))
  else:
    reset_tty()
  return 0


def reset_tty(fd: int = 1) -> None:  #{{{1
  """Resets the terminal without clearing it.

Does nothing if the given file descriptor (standard output by default)
is not a TTY, or if the platform is unsupported.

"""

  # based on code from toybox, which is 0BSD licensed:
  # <https://github.com/landley/toybox/blob/9cde583/LICENSE>

  term = open(int(fd), "wb", closefd=False)
  if not term.isatty():
    return

  try:
    import termios
    import tty
  except ImportError:
    return

  tf = TFlags()

  # <https://github.com/landley/toybox/blob/9cde583/toys/other/reset.c>
  term.write(
    #b"\x1bc"  # reset terminal; this clears the screen, which we don't want
    b"\x1b[?7h"  # DEC private mode set enable wraparound sequence
  )
  term.flush()

  # <https://github.com/landley/toybox/blob/9cde583/lib/tty.c#L109-L141>
  tty.setraw(fd, termios.TCSANOW)
  iflag, oflag, cflag, lflag, ispeed, ospeed, cc = termios.tcgetattr(fd)
  iflag |= tf.ICRNL|tf.IUTF8|tf.IXANY
  oflag |= tf.OPOST|tf.ONLCR
  cflag |= tf.CS8|tf.CREAD
  lflag |= tf.ISIG|tf.ICANON|tf.ECHO|tf.ECHOE|tf.ECHOK|tf.ECHOCTL|tf.ECHOKE|tf.IEXTEN
  termios.tcsetattr(fd, termios.TCSANOW, [iflag, oflag, cflag, lflag, ispeed, ospeed, cc])

  # <https://github.com/landley/toybox/blob/9cde583/lib/tty.c#L271>
  term.write(
    b"\x1b[?25h"  # show cursor
    b"\x1b[0m"  # reset display attributes
    #b"\x1b[999H"  # move cursor to row 999, column 0; we don't want this
    b"\x1b[K"  # delete to EOL
  )
  term.flush()


class TFlags:  #{{{1
  """A convenience class to access terminal flags, including some not supported by :mod:`termios`.

Attribute accesses for unknown terminal flags, or on unsupported platforms,
will return ``0``.

"""

  import types as _types
  _termios: _types.ModuleType | None
  try:
    import termios as _termios
  except ImportError:
    _termios = None

  def __getattribute__(self, name):
    if name.startswith("_"):
      return object.__getattribute__(self, name)
    elif name == "IUTF8":
      return self._get_iutf8()
    else:
      try:
        return self._termios.__getattribute__(name)
      except AttributeError:
        return 0

  @staticmethod
  def _get_iutf8(platform: str | None = None) -> int:
    """Returns the value of the IUTF8 termios input flag for the current or given platform.
  
  If a platform is given, it should be a string that :data:`sys.platform` would be.
  
  Returns 0 if this function does not know the value of IUTF8 for the platform.
  
  """
    try:
      # See if the Python stdlib has added support for IUTF8
      if platform:
        # ... but not if the caller gave a platform
        raise AttributeError
      import termios
      return termios.IUTF8  # type: ignore
    except (ImportError, AttributeError):
      import sys
      platform = platform or sys.platform
      if platform.startswith("linux"):
        # <https://github.com/torvalds/linux/blob/master/include/uapi/asm-generic/termbits.h>
        return 0x4000
      if platform.startswith("freebsd"):
        # <https://github.com/freebsd/freebsd-src/blob/main/sys/sys/_termios.h>
        return 0x00004000
      if platform.startswith("darwin"):
        # <https://github.com/apple-oss-distributions/xnu/blob/main/bsd/sys/termios.h>
        return 0x00004000
      return 0


if __name__ == "__main__":  #{{{1
  import sys
  try:
    sys.exit(main(sys.argv))
  except KeyboardInterrupt:
    pass