pty — Pseudo-terminal utilities¶

Source code:Lib/pty.py

Thepty module defines operations for handling the pseudo-terminalconcept: starting another process and being able to write to and read from itscontrolling terminal programmatically.

Because pseudo-terminal handling is highly platform dependent, there is code todo it only for Linux. (The Linux code is supposed to work on other platforms,but hasn’t been tested yet.)

Thepty module defines the following functions:

pty.fork()¶

Fork. Connect the child’s controlling terminal to a pseudo-terminal. Returnvalue is(pid,fd). Note that the child getspid 0, and thefd isinvalid. The parent’s return value is thepid of the child, andfd is afile descriptor connected to the child’s controlling terminal (and also to thechild’s standard input and output).

pty.openpty()¶

Open a new pseudo-terminal pair, usingos.openpty() if possible, oremulation code for generic Unix systems. Return a pair of file descriptors(master,slave), for the master and the slave end, respectively.

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

Spawn a process, and connect its controlling terminal with the currentprocess’s standard io. This is often used to baffle programs which insist onreading from the controlling terminal. It is expected that the processspawned behind the pty will eventually terminate, and when it doesspawnwill return.

The functionsmaster_read andstdin_read are passed a file descriptorwhich they should read from, and they should always return a byte string. Inorder to force spawn to return before the child process exits anOSError should be thrown.

The default implementation for both functions will read and return up to 1024bytes each time the function is called. Themaster_read callback is passedthe pseudoterminal’s master file descriptor to read output from the childprocess, andstdin_read is passed file descriptor 0, to read from theparent process’s standard input.

Returning an empty byte string from either callback is interpreted as anend-of-file (EOF) condition, and that callback will not be called afterthat. Ifstdin_read signals EOF the controlling terminal can no longercommunicate with the parent process OR the child process. Unless the childprocess will quit without any input,spawn will then loop forever. Ifmaster_read signals EOF the same behavior results (on linux at least).

If both callbacks signal EOF thenspawn will probably never return, unlessselect throws an error on your platform when passed three empty lists. Thisis a bug, documented inissue 26228.

Return the exit status value fromos.waitpid() on the child process.

waitstatus_to_exitcode() can be used to convert the exit status intoan exit code.

Raises anauditing eventpty.spawn with argumentargv.

Changed in version 3.4:spawn() now returns the status value fromos.waitpid()on the child process.

importargparseimportosimportptyimportsysimporttimeparser=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.executableifoptions.use_pythonelseos.environ.get('SHELL','sh')filename=options.filenamemode='ab'ifoptions.appendelse'wb'withopen(filename,mode)asscript:defread(fd):data=os.read(fd,1024)script.write(data)returndataprint('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)