clf.py 文件源码

def listen(self, target, timeout):
        """Listen for *timeout* seconds to become initialized as a
        *target*. The *target* must be one of :class:`nfc.clf.TTA`,
        :class:`nfc.clf.TTB`, :class:`nfc.clf.TTF`, or
        :class:`nfc.clf.DEP` (note that target type support depends on
        the hardware capabilities). The return value is :const:`None`
        if *timeout* elapsed without activation or a tuple (target,
        command) where target is the activated target (which may
        differ from the requested target, see below) and command is
        the first command received from the initiator.

        If an activated target is returned, the target type and
        attributes may differ from the *target* requested. This is
        especically true if activation as a :class:`nfc.clf.DEP`
        target is requested but the contactless frontend does not have
        a hardware implementation of the data exchange protocol and
        returns a :class:`nfc.clf.TTA` or :class:`nfc.clf.TTF` target
        instead.

        .. note:: This is a direct interface to the
           driver and not needed if :meth:`connect` is used.
        """
        if self.dev is None:
            raise IOError(errno.ENODEV, os.strerror(errno.ENODEV))

        with self.lock:
            log.debug("listen for {0:.3f} sec as target {1}"
                      .format(timeout, target))

            if type(target) is TTA:
                return self.dev.listen_tta(target, timeout)
            if type(target) is TTB:
                return self.dev.listen_ttb(target, timeout)
            if type(target) is TTF:
                return self.dev.listen_ttf(target, timeout)
            if type(target) is DEP:
                return self.dev.listen_dep(target, timeout)