How to use the pyroute2.common.basestring function in pyroute2

def test_idx_types(self):
        assert all(isinstance(i, int) for i in self.ip.by_index.keys())
        assert all(isinstance(i, basestring) for i in self.ip.by_name.keys())

def test_reprs(self):
        assert isinstance(repr(self.ip.lo.ipaddr), basestring)
        assert isinstance(repr(self.ip.lo), basestring)

def __getitem__(self, key):
        if isinstance(key, (tuple, list)):
            return self.raw[key]
        elif isinstance(key, int):
            return self.raw[tuple(self.raw.keys())[key]]
        elif isinstance(key, basestring):
            key = key.split('/')
            key = (key[0], int(key[1]))
            return self.raw[key]
        else:
            TypeError('wrong key type')

def adjust_spec(cls, spec):
        if isinstance(spec, basestring):
            ret = {'target': 'localhost'}
            ret['address'], prefixlen = spec.split('/')
            ret['prefixlen'] = int(prefixlen)
            return ret
        return spec

if header['type'] == 'seg6local':
            # Init step
            ret = {}
            table = None
            nh4 = None
            nh6 = None
            iif = None  # Actually not used
            oif = None
            srh = {}
            segs = []
            hmac = None
            # Parse segs
            if srh:
                segs = header['srh']['segs']
                # If they are in the form in_addr6,in_addr6
                if isinstance(segs, basestring):
                    # Create an array with the splitted values
                    temp = segs.split(',')
                    # Init segs
                    segs = []
                    # Iterate over the values
                    for seg in temp:
                        # Discard empty string
                        if seg != '':
                            # Add seg to segs
                            segs.append(seg)
                # hmac is optional and contains the hmac key
                hmac = header.get('hmac', None)
            # Retrieve action
            action = header['action']
            if action == 'End.X':
                # Retrieve nh6

                            constraint=lambda k, v: isinstance(k, basestring))
        self.by_index = View(src=self.interfaces,

reverse=True)
                # 8<--------------------------------------
                for i in rip:
                    # When you remove a primary IP addr, all the
                    # subnetwork can be removed. In this case you
                    # will fail, but it is OK, no need to roll back
                    try:
                        run(nl.addr, 'delete', self['index'], i[0], i[1])
                    except NetlinkError as x:
                        # bypass only errno 99,
                        # 'Cannot assign address'
                        if x.code != errno.EADDRNOTAVAIL:
                            raise
                    except socket.error as x:
                        # bypass illegal IP requests
                        if isinstance(x.args[0], basestring) and \
                                x.args[0].startswith('illegal IP'):
                            continue
                        raise
                ###
                # Add addresses
                # 8<--------------------------------------
                for i in ip2add:
                    # Try to fetch additional address attributes
                    try:
                        kwarg = dict([k for k
                                      in transaction['ipaddr'][i].items()
                                      if k[0] in ('broadcast',
                                                  'anycast',
                                                  'scope')])
                    except KeyError:
                        kwarg = None

def parse(self):
        if hasattr(self.stream, 'readlines'):
            for text in self.stream.readlines():
                self.parse_string(text)
        elif isinstance(self.stream, basestring):
            self.parse_string(self.stream)
        else:
            raise ValueError('unsupported stream')
        self.parsed = True

def decode(self):
        self.data_length = struct.unpack('B', self.buf[self.offset + 1:
                                                       self.offset + 2])[0]
        if self.policy is not None:
            if self.policy['format'] == 'string':
                fmt = '%is' % self.data_length
            else:
                fmt = self.policy['format']
            value = struct.unpack(fmt, self.buf[self.offset + 2:
                                                self.offset + 2 +
                                                self.data_length])
            if len(value) == 1:
                value = value[0]
            value = self.policy.get('decode', lambda x: x)(value)
            if isinstance(value, basestring) and \
                    self.policy['format'] == 'string':
                value = value[:value.find('\x00')]
            self.value = value
        else:
            # remember current offset as msg.decode() will advance it
            offset = self.offset
            # move past the code and option length bytes so that msg.decode()
            # starts parsing at the right location
            self.offset += 2
            msg.decode(self)
            # restore offset so that dhcpmsg.decode() advances it correctly
            self.offset = offset

        return self

def apply(self, rollback=False, fallback=False):
        # translate string link references into numbers
        for key in ('link', ):
            if key in self and isinstance(self[key], basestring):
                self[key] = self.ndb.interfaces[self[key]]['index']
        try:
            super(Interface, self).apply(rollback)
        except NetlinkError as e:
            if e.code == 95 and \
                    'master' in self and \
                    self.state == 'invalid':
                key = dict(self)
                key['create'] = True
                del key['master']
                fb = type(self)(self.view, key)
                fb.register()
                fb.apply(rollback)
                fb.set('master', self['master'])
                fb.apply(rollback)
                del fb