1:mod:`!pty` --- Pseudo-terminal utilities 2========================================= 3 4.. module:: pty 5 :platform: Unix 6 :synopsis: Pseudo-Terminal Handling for Unix. 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 19.. availability:: Unix. 20 21Pseudo-terminal handling is highly platform dependent. This code is mainly 22tested on Linux, FreeBSD, and macOS (it is supposed to work on other POSIX 23platforms but it's not been thoroughly tested). 24 25The :mod:`pty` module defines the following functions: 26 27 28.. function:: fork() 29 30 Fork. Connect the child's controlling terminal to a pseudo-terminal. Return 31 value is ``(pid, fd)``. Note that the child gets *pid* 0, and the *fd* is 32 *invalid*. The parent's return value is the *pid* of the child, and *fd* is a 33 file descriptor connected to the child's controlling terminal (and also to the 34 child's standard input and output). 35 36 .. warning:: On macOS the use of this function is unsafe when mixed with using 37 higher-level system APIs, and that includes using :mod:`urllib.request`. 38 39 40.. function:: openpty() 41 42 Open a new pseudo-terminal pair, using :func:`os.openpty` if possible, or 43 emulation code for generic Unix systems. Return a pair of file descriptors 44 ``(master, slave)``, for the master and the slave end, respectively. 45 46 47.. function:: spawn(argv[, master_read[, stdin_read]]) 48 49 Spawn a process, and connect its controlling terminal with the current 50 process's standard io. This is often used to baffle programs which insist on 51 reading from the controlling terminal. It is expected that the process 52 spawned behind the pty will eventually terminate, and when it does *spawn* 53 will return. 54 55 A loop copies STDIN of the current process to the child and data received 56 from the child to STDOUT of the current process. It is not signaled to the 57 child if STDIN of the current process closes down. 58 59 The functions *master_read* and *stdin_read* are passed a file descriptor 60 which they should read from, and they should always return a byte string. In 61 order to force spawn to return before the child process exits an 62 empty byte array should be returned to signal end of file. 63 64 The default implementation for both functions will read and return up to 1024 65 bytes each time the function is called. The *master_read* callback is passed 66 the pseudoterminal’s master file descriptor to read output from the child 67 process, and *stdin_read* is passed file descriptor 0, to read from the 68 parent process's standard input. 69 70 Returning an empty byte string from either callback is interpreted as an 71 end-of-file (EOF) condition, and that callback will not be called after 72 that. If *stdin_read* signals EOF the controlling terminal can no longer 73 communicate with the parent process OR the child process. Unless the child 74 process will quit without any input, *spawn* will then loop forever. If 75 *master_read* signals EOF the same behavior results (on linux at least). 76 77 Return the exit status value from :func:`os.waitpid` on the child process. 78 79 :func:`os.waitstatus_to_exitcode` can be used to convert the exit status into 80 an exit code. 81 82 .. audit-event:: pty.spawn argv pty.spawn 83 84 .. versionchanged:: 3.4 85 :func:`spawn` now returns the status value from :func:`os.waitpid` 86 on the child process. 87 88Example 89------- 90 91.. sectionauthor:: Steen Lumholt 92 93The following program acts like the Unix command :manpage:`script(1)`, using a 94pseudo-terminal to record all input and output of a terminal session in a 95"typescript". :: 96 97 import argparse 98 import os 99 import pty 100 import sys 101 import time 102 103 parser = argparse.ArgumentParser() 104 parser.add_argument('-a', dest='append', action='store_true') 105 parser.add_argument('-p', dest='use_python', action='store_true') 106 parser.add_argument('filename', nargs='?', default='typescript') 107 options = parser.parse_args() 108 109 shell = sys.executable if options.use_python else os.environ.get('SHELL', 'sh') 110 filename = options.filename 111 mode = 'ab' if options.append else 'wb' 112 113 with open(filename, mode) as script: 114 def read(fd): 115 data = os.read(fd, 1024) 116 script.write(data) 117 return data 118 119 print('Script started, file is', filename) 120 script.write(('Script started on %s\n' % time.asctime()).encode()) 121 122 pty.spawn(shell, read) 123 124 script.write(('Script done on %s\n' % time.asctime()).encode()) 125 print('Script done, file is', filename) 126