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Lib/tty.py

cpython 3.14 @ ab2d84fe1023/Lib/tty.py

tty.py is a thin convenience layer over termios. It provides three functions that put a terminal file descriptor into raw or cbreak mode. Raw mode disables virtually all terminal line-discipline processing (echo, canonical buffering, signal generation, output post-processing). Cbreak mode is the same except that signal-generating characters (Ctrl-C, Ctrl-Z) are still processed. Both modes are reversible by saving the original termios attribute list before calling into this module. cfmakeraw encapsulates the flag arithmetic so callers do not have to remember which bits to clear.

Map​

LinesSymbolRolegopy
1-8module docstring, importsImports termios and tty constants (IFLAG, OFLAG, CFLAG, LFLAG, ISPEED, OSPEED, CC)not ported
10-18cfmakeraw(mode)Mutates a termios attribute list in-place to raw settings. No I/O.not ported
20-30setraw(fd, when=TCSAFLUSH)Reads current termios, calls cfmakeraw, applies with tcsetattr.not ported
32-42setcbreak(fd, when=TCSAFLUSH)Like setraw but leaves ISIG set so Ctrl-C/Z still work.not ported

Reading​

Module-level constants (lines 1 to 8)​

cpython 3.14 @ ab2d84fe1023/Lib/tty.py#L1-8

The file imports the six index constants (IFLAG, OFLAG, CFLAG, LFLAG, ISPEED, OSPEED, CC) from termios and re-exports them. These are positional indices into the list returned by termios.tcgetattr. Using named constants rather than bare integers makes the flag manipulation in cfmakeraw and setcbreak readable at a glance.

from termios import (
    IFLAG, OFLAG, CFLAG, LFLAG, ISPEED, OSPEED, CC,
    TCSAFLUSH, tcgetattr, tcsetattr,
)

cfmakeraw (lines 10 to 18)​

cpython 3.14 @ ab2d84fe1023/Lib/tty.py#L10-18

cfmakeraw mirrors the POSIX cfmakeraw(3) C function. It receives the list that tcgetattr returns, clears the relevant bits, and returns the mutated list. The caller is responsible for the actual tcsetattr call, which keeps the function pure and easy to test.

def cfmakeraw(mode):
    mode[IFLAG] = mode[IFLAG] & ~(IGNBRK | BRKINT | PARMRK | ISTRIP |
                                   INLCR | IGNCR | ICRNL | IXON)
    mode[OFLAG] = mode[OFLAG] & ~OPOST
    mode[CFLAG] = (mode[CFLAG] & ~(CSIZE | PARENB)) | CS8
    mode[LFLAG] = mode[LFLAG] & ~(ECHO | ECHONL | ICANON | ISIG | IEXTEN)
    mode[CC][VMIN] = 1
    mode[CC][VTIME] = 0
    return mode

The key effect is that reads return as soon as one byte arrives (VMIN=1, VTIME=0) and no characters are echoed or interpreted by the kernel.

setraw and setcbreak (lines 20 to 42)​

cpython 3.14 @ ab2d84fe1023/Lib/tty.py#L20-42

Both functions follow the same pattern: save the old attribute list, build a modified copy, apply it. The only difference is that setcbreak omits clearing ISIG, so SIGINT and SIGTSTP are still raised on Ctrl-C and Ctrl-Z.

def setraw(fd, when=TCSAFLUSH):
    mode = tcgetattr(fd)
    mode = cfmakeraw(mode)
    tcsetattr(fd, when, mode)

def setcbreak(fd, when=TCSAFLUSH):
    mode = tcgetattr(fd)
    mode[LFLAG] = mode[LFLAG] & ~(ECHO | ICANON | IEXTEN)
    mode[CC][VMIN] = 1
    mode[CC][VTIME] = 0
    tcsetattr(fd, when, mode)

when=TCSAFLUSH means the change takes effect after all pending output has been written and any unread input is discarded. Callers that want an immediate change pass TCSANOW.

gopy mirror​

Not yet ported.

The termios module is a thin wrapper over the POSIX <termios.h> C API. gopy does not yet expose that API, so tty.py cannot be ported until a termios module is available. When that work lands, cfmakeraw, setraw, and setcbreak translate directly as Go functions accepting a file descriptor integer.

CPython 3.14 changes​

CPython 3.14 extracted the flag arithmetic into the new cfmakeraw function (previously the bit manipulation was inlined inside setraw). The public signatures of setraw and setcbreak are unchanged. The addition of cfmakeraw as a named export makes the module testable without a real terminal file descriptor.