# Source code for rdflib.plugins.serializers.nt

    """
    N-Triples RDF graph serializer for RDFLib.
    See <http://www.w3.org/TR/rdf-testcases/#ntriples> for details about the
    format.
    """
    from rdflib.term import Literal
    from rdflib.serializer import Serializer
    from rdflib.py3compat import b
    import warnings

    __all__ = ['NTSerializer']

    class NTSerializer(Serializer):
        """
        Serializes RDF graphs to NTriples format.
        """

        def serialize(self, stream, base=None, encoding=None, **args):
            if base is not None:
                warnings.warn("NTSerializer does not support base.")
            if encoding is not None:
                warnings.warn("NTSerializer does not use custom encoding.")
            encoding = self.encoding
            for triple in self.store:
                stream.write(_nt_row(triple).encode(encoding, "replace"))
            stream.write(b("\n"))

    def _nt_row(triple):
        if isinstance(triple[2], Literal):
            return u"%s %s %s .\n" % (
                triple[0].n3(),
                triple[1].n3(),
                _xmlcharref_encode(_quoteLiteral(triple[2])))
        else:
            return u"%s %s %s .\n" % (triple[0].n3(),
                                      triple[1].n3(),
                                      _xmlcharref_encode(triple[2].n3()))

    def _quoteLiteral(l):
        '''
        a simpler version of term.Literal.n3()
        '''

        encoded = _quote_encode(l)

        if l.language:
            if l.datatype:
                raise Exception("Literal has datatype AND language!")
            return '%s@%s' % (encoded, l.language)
        elif l.datatype:
            return '%s^^<%s>' % (encoded, l.datatype)
        else:
            return '%s' % encoded

    def _quote_encode(l):
        return '"%s"' % l.replace('\\', '\\\\')\
            .replace('\n', '\\n')\
            .replace('"', '\\"')\
            .replace('\r', '\\r')

    # from <http://code.activestate.com/recipes/303668/>
    def _xmlcharref_encode(unicode_data, encoding="ascii"):
        """Emulate Python 2.3's 'xmlcharrefreplace' encoding error handler."""
        res = ""

        # Step through the unicode_data string one character at a time in
        # order to catch unencodable characters:
        for char in unicode_data:
            try:
                char.encode(encoding, 'strict')
            except UnicodeError:
                if ord(char) <= 0xFFFF:
                    res += '\\u%04X' % ord(char)
                else:
                    res += '\\U%08X' % ord(char)
            else:
                res += char

        return res