ptyprocess.py 文件源码

def _make_eof_intr():
    """Set constants _EOF and _INTR.

    This avoids doing potentially costly operations on module load.
    """
    global _EOF, _INTR
    if (_EOF is not None) and (_INTR is not None):
        return

    # inherit EOF and INTR definitions from controlling process.
    try:
        from termios import VEOF, VINTR
        try:
            fd = sys.__stdin__.fileno()
        except ValueError:
            # ValueError: I/O operation on closed file
            fd = sys.__stdout__.fileno()
        intr = ord(termios.tcgetattr(fd)[6][VINTR])
        eof = ord(termios.tcgetattr(fd)[6][VEOF])
    except (ImportError, OSError, IOError, ValueError, termios.error):
        # unless the controlling process is also not a terminal,
        # such as cron(1), or when stdin and stdout are both closed.
        # Fall-back to using CEOF and CINTR. There
        try:
            from termios import CEOF, CINTR
            (intr, eof) = (CINTR, CEOF)
        except ImportError:
            #                         ^C, ^D
            (intr, eof) = (3, 4)

    _INTR = _byte(intr)
    _EOF = _byte(eof)