1:mod:`pty` --- Pseudo-terminal utilities 2======================================== 3 4.. module:: pty 5 :platform: Linux 6 :synopsis: Pseudo-Terminal Handling for Linux. 7 8.. moduleauthor:: Steen Lumholt 9.. sectionauthor:: Moshe Zadka <moshez@zadka.site.co.il> 10 11**Source code:** :source:`Lib/pty.py` 12 13-------------- 14 15The :mod:`pty` module defines operations for handling the pseudo-terminal 16concept: starting another process and being able to write to and read from its 17controlling terminal programmatically. 18 19Because pseudo-terminal handling is highly platform dependent, there is code to 20do it only for Linux. (The Linux code is supposed to work on other platforms, 21but hasn't been tested yet.) 22 23The :mod:`pty` module defines the following functions: 24 25 26.. function:: fork() 27 28 Fork. Connect the child's controlling terminal to a pseudo-terminal. Return 29 value is ``(pid, fd)``. Note that the child gets *pid* 0, and the *fd* is 30 *invalid*. The parent's return value is the *pid* of the child, and *fd* is a 31 file descriptor connected to the child's controlling terminal (and also to the 32 child's standard input and output). 33 34 35.. function:: openpty() 36 37 Open a new pseudo-terminal pair, using :func:`os.openpty` if possible, or 38 emulation code for generic Unix systems. Return a pair of file descriptors 39 ``(master, slave)``, for the master and the slave end, respectively. 40 41 42.. function:: spawn(argv[, master_read[, stdin_read]]) 43 44 Spawn a process, and connect its controlling terminal with the current 45 process's standard io. This is often used to baffle programs which insist on 46 reading from the controlling terminal. It is expected that the process 47 spawned behind the pty will eventually terminate, and when it does *spawn* 48 will return. 49 50 The functions *master_read* and *stdin_read* are passed a file descriptor 51 which they should read from, and they should always return a byte string. In 52 order to force spawn to return before the child process exits an 53 :exc:`OSError` should be thrown. 54 55 The default implementation for both functions will read and return up to 1024 56 bytes each time the function is called. The *master_read* callback is passed 57 the pseudoterminal’s master file descriptor to read output from the child 58 process, and *stdin_read* is passed file descriptor 0, to read from the 59 parent process's standard input. 60 61 Returning an empty byte string from either callback is interpreted as an 62 end-of-file (EOF) condition, and that callback will not be called after 63 that. If *stdin_read* signals EOF the controlling terminal can no longer 64 communicate with the parent process OR the child process. Unless the child 65 process will quit without any input, *spawn* will then loop forever. If 66 *master_read* signals EOF the same behavior results (on linux at least). 67 68 If both callbacks signal EOF then *spawn* will probably never return, unless 69 *select* throws an error on your platform when passed three empty lists. This 70 is a bug, documented in `issue 26228 <https://bugs.python.org/issue26228>`_. 71 72 .. audit-event:: pty.spawn argv pty.spawn 73 74 .. versionchanged:: 3.4 75 :func:`spawn` now returns the status value from :func:`os.waitpid` 76 on the child process. 77 78Example 79------- 80 81.. sectionauthor:: Steen Lumholt 82 83The following program acts like the Unix command :manpage:`script(1)`, using a 84pseudo-terminal to record all input and output of a terminal session in a 85"typescript". :: 86 87 import argparse 88 import os 89 import pty 90 import sys 91 import time 92 93 parser = argparse.ArgumentParser() 94 parser.add_argument('-a', dest='append', action='store_true') 95 parser.add_argument('-p', dest='use_python', action='store_true') 96 parser.add_argument('filename', nargs='?', default='typescript') 97 options = parser.parse_args() 98 99 shell = sys.executable if options.use_python else os.environ.get('SHELL', 'sh') 100 filename = options.filename 101 mode = 'ab' if options.append else 'wb' 102 103 with open(filename, mode) as script: 104 def read(fd): 105 data = os.read(fd, 1024) 106 script.write(data) 107 return data 108 109 print('Script started, file is', filename) 110 script.write(('Script started on %s\n' % time.asctime()).encode()) 111 112 pty.spawn(shell, read) 113 114 script.write(('Script done on %s\n' % time.asctime()).encode()) 115 print('Script done, file is', filename) 116