"pty" --- 擬似端末ユーティリティ
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**ソースコード:** Lib/pty.py

======================================================================

"pty" モジュールは擬似端末(他のプロセスを実行してその制御をしている端
末をプログラムで読み書きする)を制御する操作を定義しています。

利用可能な環境: Unix。

Pseudo-terminal handling is highly platform dependent. This code is
mainly tested on Linux, FreeBSD, and macOS (it is supposed to work on
other POSIX platforms but it's not been thoroughly tested).

"pty" モジュールでは以下の関数を定義しています:

pty.fork()

   forkします。子プロセスの制御端末を擬似端末に接続します。返り値は
   "(pid, fd)" です。子プロセスは *pid* として0、*fd* として *invalid*
   をそれぞれ受けとります。親プロセスは *pid* として子プロセスのPID、
   *fd* として子プロセスの制御端末 (子プロセスの標準入出力に接続されて
   いる)のファイル記述子を受けとります。

   警告:

     On macOS the use of this function is unsafe when mixed with using
     higher-level system APIs, and that includes using
     "urllib.request".

pty.openpty()

   新しい擬似端末のペアを開きます。利用できるなら "os.openpty()" を使
   い、利用できなければ一般的なUnixシステム用のエミュレーションコード
   を使います。マスター、スレーブそれぞれのためのファイル記述子、
   "(master, slave)" のタプルを返します。

pty.spawn(argv[, master_read[, stdin_read]])

   Spawn a process, and connect its controlling terminal with the
   current process's standard io. This is often used to baffle
   programs which insist on reading from the controlling terminal. It
   is expected that the process spawned behind the pty will eventually
   terminate, and when it does *spawn* will return.

   A loop copies STDIN of the current process to the child and data
   received from the child to STDOUT of the current process. It is not
   signaled to the child if STDIN of the current process closes down.

   The functions *master_read* and *stdin_read* are passed a file
   descriptor which they should read from, and they should always
   return a byte string. In order to force spawn to return before the
   child process exits an empty byte array should be returned to
   signal end of file.

   The default implementation for both functions will read and return
   up to 1024 bytes each time the function is called. The
   *master_read* callback is passed the pseudoterminal’s master file
   descriptor to read output from the child process, and *stdin_read*
   is passed file descriptor 0, to read from the parent process's
   standard input.

   Returning an empty byte string from either callback is interpreted
   as an end-of-file (EOF) condition, and that callback will not be
   called after that. If *stdin_read* signals EOF the controlling
   terminal can no longer communicate with the parent process OR the
   child process. Unless the child process will quit without any
   input, *spawn* will then loop forever. If *master_read* signals EOF
   the same behavior results (on linux at least).

   Return the exit status value from "os.waitpid()" on the child
   process.

   "os.waitstatus_to_exitcode()" can be used to convert the exit
   status into an exit code.

   Raises an auditing event "pty.spawn" with argument "argv".

   バージョン 3.4 で変更: "spawn()" が "os.waitpid()" が返す子プロセス
   のステータス値を返すようになりました。


使用例
======

下記のプログラムは Unix コマンド *script(1)* のように動作します。疑似
端末を使用して、端末セッションのすべての入出力を "typescript" に記録し
ます。

   import argparse
   import os
   import pty
   import sys
   import time

   parser = argparse.ArgumentParser()
   parser.add_argument('-a', dest='append', action='store_true')
   parser.add_argument('-p', dest='use_python', action='store_true')
   parser.add_argument('filename', nargs='?', default='typescript')
   options = parser.parse_args()

   shell = sys.executable if options.use_python else os.environ.get('SHELL', 'sh')
   filename = options.filename
   mode = 'ab' if options.append else 'wb'

   with open(filename, mode) as script:
       def read(fd):
           data = os.read(fd, 1024)
           script.write(data)
           return data

       print('Script started, file is', filename)
       script.write(('Script started on %s\n' % time.asctime()).encode())

       pty.spawn(shell, read)

       script.write(('Script done on %s\n' % time.asctime()).encode())
       print('Script done, file is', filename)
