serialposix.py 文件源码

def read(self, size=1):
        """Read size bytes from the serial port. If a timeout is set it may
           return less characters as requested. With no timeout it will block
           until the requested number of bytes is read."""
        if self.fd is None: raise portNotOpenError
        read = bytearray()
        poll = select.poll()
        poll.register(self.fd, select.POLLIN|select.POLLERR|select.POLLHUP|select.POLLNVAL)
        if size > 0:
            while len(read) < size:
                # print "\tread(): size",size, "have", len(read)    #debug
                # wait until device becomes ready to read (or something fails)
                for fd, event in poll.poll(self._timeout*1000):
                    if event & (select.POLLERR|select.POLLHUP|select.POLLNVAL):
                        raise SerialException('device reports error (poll)')
                    #  we don't care if it is select.POLLIN or timeout, that's
                    #  handled below
                buf = os.read(self.fd, size - len(read))
                read.extend(buf)
                if ((self._timeout is not None and self._timeout >= 0) or 
                    (self._interCharTimeout is not None and self._interCharTimeout > 0)) and not buf:
                    break   # early abort on timeout
        return bytes(read)