'This method returns the VCard data in its native format.
Note: the output is a string of bytes, not unicode characters.
>>> print SimpleVCard().as_vCard()
BEGIN:VCARD
VERSION:4.0
FN:Anonymous
END:VCARD'

def as_vCard(self):

    for key in self.VCARD4_REQUIRED:
        with self._lock:
            if (not self.get_all(key)):
                default = self.VCARD4_KEYS[key][2]
                self._lines[:0] = [VCardLine(name=key, value=default)]
    with self._lock:
        self._sort_lines()
        return '\n'.join(((['BEGIN:VCARD'] + [l.as_vcardline() for l in self._lines if l]) + ['END:VCARD']))
