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      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 (a] zadka.site.co.il>
     10 
     11 **Source code:** :source:`Lib/pty.py`
     12 
     13 --------------
     14 
     15 The :mod:`pty` module defines operations for handling the pseudo-terminal
     16 concept: starting another process and being able to write to and read from its
     17 controlling terminal programmatically.
     18 
     19 Because pseudo-terminal handling is highly platform dependent, there is code to
     20 do it only for Linux. (The Linux code is supposed to work on other platforms,
     21 but hasn't been tested yet.)
     22 
     23 The :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.
     47 
     48    The functions *master_read* and *stdin_read* should be functions which read from
     49    a file descriptor. The defaults try to read 1024 bytes each time they are
     50    called.
     51 
     52    .. versionchanged:: 3.4
     53       :func:`spawn` now returns the status value from :func:`os.waitpid`
     54       on the child process.
     55 
     56 Example
     57 -------
     58 
     59 .. sectionauthor:: Steen Lumholt
     60 
     61 The following program acts like the Unix command :manpage:`script(1)`, using a
     62 pseudo-terminal to record all input and output of a terminal session in a
     63 "typescript". ::
     64 
     65     import argparse
     66     import os
     67     import pty
     68     import sys
     69     import time
     70 
     71     parser = argparse.ArgumentParser()
     72     parser.add_argument('-a', dest='append', action='store_true')
     73     parser.add_argument('-p', dest='use_python', action='store_true')
     74     parser.add_argument('filename', nargs='?', default='typescript')
     75     options = parser.parse_args()
     76 
     77     shell = sys.executable if options.use_python else os.environ.get('SHELL', 'sh')
     78     filename = options.filename
     79     mode = 'ab' if options.append else 'wb'
     80 
     81     with open(filename, mode) as script:
     82         def read(fd):
     83             data = os.read(fd, 1024)
     84             script.write(data)
     85             return data
     86 
     87         print('Script started, file is', filename)
     88         script.write(('Script started on %s\n' % time.asctime()).encode())
     89 
     90         pty.spawn(shell, read)
     91 
     92         script.write(('Script done on %s\n' % time.asctime()).encode())
     93         print('Script done, file is', filename)
     94