Python dns.rdata() Examples

def iterate_rdatas(self, rdtype=dns.rdatatype.ANY,
                       covers=dns.rdatatype.NONE):
        """Return a generator which yields (name, ttl, rdata) tuples for
        all rdatas in the zone which have the specified I{rdtype}
        and I{covers}.  If I{rdtype} is dns.rdatatype.ANY, the default,
        then all rdatas will be matched.

        @param rdtype: int or string
        @type rdtype: int or string
        @param covers: the covered type (defaults to None)
        @type covers: int or string
        """

        if isinstance(rdtype, string_types):
            rdtype = dns.rdatatype.from_text(rdtype)
        if isinstance(covers, string_types):
            covers = dns.rdatatype.from_text(covers)
        for (name, node) in self.iteritems():
            for rds in node:
                if rdtype == dns.rdatatype.ANY or \
                   (rds.rdtype == rdtype and rds.covers == covers):
                    for rdata in rds:
                        yield (name, rds.ttl, rdata) 

def from_text_list(rdclass, rdtype, ttl, text_rdatas):
    """Create an rdataset with the specified class, type, and TTL, and with
    the specified list of rdatas in text format.

    @rtype: dns.rdataset.Rdataset object
    """

    if isinstance(rdclass, string_types):
        rdclass = dns.rdataclass.from_text(rdclass)
    if isinstance(rdtype, string_types):
        rdtype = dns.rdatatype.from_text(rdtype)
    r = Rdataset(rdclass, rdtype)
    r.update_ttl(ttl)
    for t in text_rdatas:
        rd = dns.rdata.from_text(r.rdclass, r.rdtype, t)
        r.add(rd)
    return r 

def from_rdata_list(ttl, rdatas):
    """Create an rdataset with the specified TTL, and with
    the specified list of rdata objects.

    @rtype: dns.rdataset.Rdataset object
    """

    if len(rdatas) == 0:
        raise ValueError("rdata list must not be empty")
    r = None
    for rd in rdatas:
        if r is None:
            r = Rdataset(rd.rdclass, rd.rdtype)
            r.update_ttl(ttl)
        r.add(rd)
    return r 

def iterate_rdatas(self, rdtype=dns.rdatatype.ANY,
                       covers=dns.rdatatype.NONE):
        """Return a generator which yields (name, ttl, rdata) tuples for
        all rdatas in the zone which have the specified I{rdtype}
        and I{covers}.  If I{rdtype} is dns.rdatatype.ANY, the default,
        then all rdatas will be matched.

        @param rdtype: int or string
        @type rdtype: int or string
        @param covers: the covered type (defaults to None)
        @type covers: int or string
        """

        if isinstance(rdtype, string_types):
            rdtype = dns.rdatatype.from_text(rdtype)
        if isinstance(covers, string_types):
            covers = dns.rdatatype.from_text(covers)
        for (name, node) in self.iteritems():
            for rds in node:
                if rdtype == dns.rdatatype.ANY or \
                   (rds.rdtype == rdtype and rds.covers == covers):
                    for rdata in rds:
                        yield (name, rds.ttl, rdata) 

def __init__(self, origin, rdclass=dns.rdataclass.IN, relativize=True):
        """Initialize a zone object.

        @param origin: The origin of the zone.
        @type origin: dns.name.Name object
        @param rdclass: The zone's rdata class; the default is class IN.
        @type rdclass: int"""

        if origin is not None:
            if isinstance(origin, string_types):
                origin = dns.name.from_text(origin)
            elif not isinstance(origin, dns.name.Name):
                raise ValueError("origin parameter must be convertible to a "
                                 "DNS name")
            if not origin.is_absolute():
                raise ValueError("origin parameter must be an absolute name")
        self.origin = origin
        self.rdclass = rdclass
        self.nodes = {}
        self.relativize = relativize 

def from_text_list(rdclass, rdtype, ttl, text_rdatas):
    """Create an rdataset with the specified class, type, and TTL, and with
    the specified list of rdatas in text format.

    @rtype: dns.rdataset.Rdataset object
    """

    if isinstance(rdclass, string_types):
        rdclass = dns.rdataclass.from_text(rdclass)
    if isinstance(rdtype, string_types):
        rdtype = dns.rdatatype.from_text(rdtype)
    r = Rdataset(rdclass, rdtype)
    r.update_ttl(ttl)
    for t in text_rdatas:
        rd = dns.rdata.from_text(r.rdclass, r.rdtype, t)
        r.add(rd)
    return r 

def from_rdata_list(ttl, rdatas):
    """Create an rdataset with the specified TTL, and with
    the specified list of rdata objects.

    @rtype: dns.rdataset.Rdataset object
    """

    if len(rdatas) == 0:
        raise ValueError("rdata list must not be empty")
    r = None
    for rd in rdatas:
        if r is None:
            r = Rdataset(rd.rdclass, rd.rdtype)
            r.update_ttl(ttl)
        r.add(rd)
    return r 

def iterate_rdatas(self, rdtype=dns.rdatatype.ANY,
                       covers=dns.rdatatype.NONE):
        """Return a generator which yields (name, ttl, rdata) tuples for
        all rdatas in the zone which have the specified I{rdtype}
        and I{covers}.  If I{rdtype} is dns.rdatatype.ANY, the default,
        then all rdatas will be matched.

        @param rdtype: int or string
        @type rdtype: int or string
        @param covers: the covered type (defaults to None)
        @type covers: int or string
        """

        if isinstance(rdtype, (str, unicode)):
            rdtype = dns.rdatatype.from_text(rdtype)
        if isinstance(covers, (str, unicode)):
            covers = dns.rdatatype.from_text(covers)
        for (name, node) in self.iteritems():
            for rds in node:
                if rdtype == dns.rdatatype.ANY or \
                   (rds.rdtype == rdtype and rds.covers == covers):
                    for rdata in rds:
                        yield (name, rds.ttl, rdata) 

def __init__(self, origin, rdclass=dns.rdataclass.IN, relativize=True):
        """Initialize a zone object.

        @param origin: The origin of the zone.
        @type origin: dns.name.Name object
        @param rdclass: The zone's rdata class; the default is class IN.
        @type rdclass: int"""

        if origin is not None:
            if isinstance(origin, string_types):
                origin = dns.name.from_text(origin)
            elif not isinstance(origin, dns.name.Name):
                raise ValueError("origin parameter must be convertible to a "
                                 "DNS name")
            if not origin.is_absolute():
                raise ValueError("origin parameter must be an absolute name")
        self.origin = origin
        self.rdclass = rdclass
        self.nodes = {}
        self.relativize = relativize 

def __init__(self, origin, rdclass=dns.rdataclass.IN, relativize=True):
        """Initialize a zone object.

        @param origin: The origin of the zone.
        @type origin: dns.name.Name object
        @param rdclass: The zone's rdata class; the default is class IN.
        @type rdclass: int"""

        if origin is not None:
            if isinstance(origin, string_types):
                origin = dns.name.from_text(origin)
            elif not isinstance(origin, dns.name.Name):
                raise ValueError("origin parameter must be convertible to a "
                                 "DNS name")
            if not origin.is_absolute():
                raise ValueError("origin parameter must be an absolute name")
        self.origin = origin
        self.rdclass = rdclass
        self.nodes = {}
        self.relativize = relativize 

def from_rdata_list(ttl, rdatas):
    """Create an rdataset with the specified TTL, and with
    the specified list of rdata objects.

    @rtype: dns.rdataset.Rdataset object
    """

    if len(rdatas) == 0:
        raise ValueError("rdata list must not be empty")
    r = None
    for rd in rdatas:
        if r is None:
            r = Rdataset(rd.rdclass, rd.rdtype)
            r.update_ttl(ttl)
            first_time = False
        r.add(rd)
    return r 

def from_text_list(rdclass, rdtype, ttl, text_rdatas):
    """Create an rdataset with the specified class, type, and TTL, and with
    the specified list of rdatas in text format.

    @rtype: dns.rdataset.Rdataset object
    """

    if isinstance(rdclass, (str, unicode)):
        rdclass = dns.rdataclass.from_text(rdclass)
    if isinstance(rdtype, (str, unicode)):
        rdtype = dns.rdatatype.from_text(rdtype)
    r = Rdataset(rdclass, rdtype)
    r.update_ttl(ttl)
    for t in text_rdatas:
        rd = dns.rdata.from_text(r.rdclass, r.rdtype, t)
        r.add(rd)
    return r 

def delete_rdataset(self, name, rdtype, covers=dns.rdatatype.NONE):
        """Delete the rdataset matching I{rdtype} and I{covers}, if it
        exists at the node specified by I{name}.

        The I{name}, I{rdtype}, and I{covers} parameters may be
        strings, in which case they will be converted to their proper
        type.

        It is not an error if the node does not exist, or if there is no
        matching rdataset at the node.

        If the node has no rdatasets after the deletion, it will itself
        be deleted.

        @param name: the owner name to look for
        @type name: DNS.name.Name object or string
        @param rdtype: the rdata type desired
        @type rdtype: int or string
        @param covers: the covered type (defaults to None)
        @type covers: int or string
        """

        name = self._validate_name(name)
        if isinstance(rdtype, string_types):
            rdtype = dns.rdatatype.from_text(rdtype)
        if isinstance(covers, string_types):
            covers = dns.rdatatype.from_text(covers)
        node = self.get_node(name)
        if node is not None:
            node.delete_rdataset(self.rdclass, rdtype, covers)
            if len(node) == 0:
                self.delete_node(name) 

def present(self, name, *args):
        """Require that an owner name (and optionally an rdata type,
        or specific rdataset) exists as a prerequisite to the
        execution of the update.  The first argument is always a name.
        The other arguments can be:

                - rdataset...

                - rdata...

                - rdtype, string..."""

        if isinstance(name, string_types):
            name = dns.name.from_text(name, None)
        if len(args) == 0:
            self.find_rrset(self.answer, name,
                            dns.rdataclass.ANY, dns.rdatatype.ANY,
                            dns.rdatatype.NONE, None,
                            True, True)
        elif isinstance(args[0], dns.rdataset.Rdataset) or \
            isinstance(args[0], dns.rdata.Rdata) or \
                len(args) > 1:
            if not isinstance(args[0], dns.rdataset.Rdataset):
                # Add a 0 TTL
                args = list(args)
                args.insert(0, 0)
            self._add(False, self.answer, name, *args)
        else:
            rdtype = args[0]
            if isinstance(rdtype, string_types):
                rdtype = dns.rdatatype.from_text(rdtype)
            self.find_rrset(self.answer, name,
                            dns.rdataclass.ANY, rdtype,
                            dns.rdatatype.NONE, None,
                            True, True) 

def replace(self, name, *args):
        """Replace records.  The first argument is always a name.  The other
        arguments can be:

                - rdataset...

                - ttl, rdata...

                - ttl, rdtype, string...

        Note that if you want to replace the entire node, you should do
        a delete of the name followed by one or more calls to add."""

        self._add(True, self.authority, name, *args) 

def add(self, name, *args):
        """Add records.  The first argument is always a name.  The other
        arguments can be:

                - rdataset...

                - ttl, rdata...

                - ttl, rdtype, string..."""
        self._add(False, self.authority, name, *args) 

def find_rdataset(self, name, rdtype, covers=dns.rdatatype.NONE,
                      create=False):
        """Look for rdata with the specified name and type in the zone,
        and return an rdataset encapsulating it.

        The I{name}, I{rdtype}, and I{covers} parameters may be
        strings, in which case they will be converted to their proper
        type.

        The rdataset returned is not a copy; changes to it will change
        the zone.

        KeyError is raised if the name or type are not found.
        Use L{get_rdataset} if you want to have None returned instead.

        @param name: the owner name to look for
        @type name: DNS.name.Name object or string
        @param rdtype: the rdata type desired
        @type rdtype: int or string
        @param covers: the covered type (defaults to None)
        @type covers: int or string
        @param create: should the node and rdataset be created if they do not
        exist?
        @type create: bool
        @raises KeyError: the node or rdata could not be found
        @rtype: dns.rrset.RRset object
        """

        name = self._validate_name(name)
        if isinstance(rdtype, string_types):
            rdtype = dns.rdatatype.from_text(rdtype)
        if isinstance(covers, string_types):
            covers = dns.rdatatype.from_text(covers)
        node = self.find_node(name, create)
        return node.find_rdataset(self.rdclass, rdtype, covers, create) 

def find_rrset(self, name, rdtype, covers=dns.rdatatype.NONE):
        """Look for rdata with the specified name and type in the zone,
        and return an RRset encapsulating it.

        The I{name}, I{rdtype}, and I{covers} parameters may be
        strings, in which case they will be converted to their proper
        type.

        This method is less efficient than the similar
        L{find_rdataset} because it creates an RRset instead of
        returning the matching rdataset.  It may be more convenient
        for some uses since it returns an object which binds the owner
        name to the rdata.

        This method may not be used to create new nodes or rdatasets;
        use L{find_rdataset} instead.

        KeyError is raised if the name or type are not found.
        Use L{get_rrset} if you want to have None returned instead.

        @param name: the owner name to look for
        @type name: DNS.name.Name object or string
        @param rdtype: the rdata type desired
        @type rdtype: int or string
        @param covers: the covered type (defaults to None)
        @type covers: int or string
        @raises KeyError: the node or rdata could not be found
        @rtype: dns.rrset.RRset object
        """

        name = self._validate_name(name)
        if isinstance(rdtype, string_types):
            rdtype = dns.rdatatype.from_text(rdtype)
        if isinstance(covers, string_types):
            covers = dns.rdatatype.from_text(covers)
        rdataset = self.nodes[name].find_rdataset(self.rdclass, rdtype, covers)
        rrset = dns.rrset.RRset(name, self.rdclass, rdtype, covers)
        rrset.update(rdataset)
        return rrset 

def to_text(self, origin=None, relativize=True, **kw):
        txt = ''
        prefix = ''
        for s in self.strings:
            txt += '%s"%s"' % (prefix, dns.rdata._escapify(s))
            prefix = ' '
        return txt 

def _add(self, replace, section, name, *args):
        """Add records.  The first argument is the replace mode.  If
        false, RRs are added to an existing RRset; if true, the RRset
        is replaced with the specified contents.  The second
        argument is the section to add to.  The third argument
        is always a name.  The other arguments can be:

                - rdataset...

                - ttl, rdata...

                - ttl, rdtype, string..."""

        if isinstance(name, string_types):
            name = dns.name.from_text(name, None)
        if isinstance(args[0], dns.rdataset.Rdataset):
            for rds in args:
                if replace:
                    self.delete(name, rds.rdtype)
                for rd in rds:
                    self._add_rr(name, rds.ttl, rd, section=section)
        else:
            args = list(args)
            ttl = int(args.pop(0))
            if isinstance(args[0], dns.rdata.Rdata):
                if replace:
                    self.delete(name, args[0].rdtype)
                for rd in args:
                    self._add_rr(name, ttl, rd, section=section)
            else:
                rdtype = args.pop(0)
                if isinstance(rdtype, string_types):
                    rdtype = dns.rdatatype.from_text(rdtype)
                if replace:
                    self.delete(name, rdtype)
                for s in args:
                    rd = dns.rdata.from_text(self.zone_rdclass, rdtype, s,
                                             self.origin)
                    self._add_rr(name, ttl, rd, section=section) 

def find_rrset(self, name, rdtype, covers=dns.rdatatype.NONE):
        """Look for rdata with the specified name and type in the zone,
        and return an RRset encapsulating it.

        The I{name}, I{rdtype}, and I{covers} parameters may be
        strings, in which case they will be converted to their proper
        type.

        This method is less efficient than the similar
        L{find_rdataset} because it creates an RRset instead of
        returning the matching rdataset.  It may be more convenient
        for some uses since it returns an object which binds the owner
        name to the rdata.

        This method may not be used to create new nodes or rdatasets;
        use L{find_rdataset} instead.

        KeyError is raised if the name or type are not found.
        Use L{get_rrset} if you want to have None returned instead.

        @param name: the owner name to look for
        @type name: DNS.name.Name object or string
        @param rdtype: the rdata type desired
        @type rdtype: int or string
        @param covers: the covered type (defaults to None)
        @type covers: int or string
        @raises KeyError: the node or rdata could not be found
        @rtype: dns.rrset.RRset object
        """

        name = self._validate_name(name)
        if isinstance(rdtype, string_types):
            rdtype = dns.rdatatype.from_text(rdtype)
        if isinstance(covers, string_types):
            covers = dns.rdatatype.from_text(covers)
        rdataset = self.nodes[name].find_rdataset(self.rdclass, rdtype, covers)
        rrset = dns.rrset.RRset(name, self.rdclass, rdtype, covers)
        rrset.update(rdataset)
        return rrset 

def delete_rdataset(self, name, rdtype, covers=dns.rdatatype.NONE):
        """Delete the rdataset matching I{rdtype} and I{covers}, if it
        exists at the node specified by I{name}.

        The I{name}, I{rdtype}, and I{covers} parameters may be
        strings, in which case they will be converted to their proper
        type.

        It is not an error if the node does not exist, or if there is no
        matching rdataset at the node.

        If the node has no rdatasets after the deletion, it will itself
        be deleted.

        @param name: the owner name to look for
        @type name: DNS.name.Name object or string
        @param rdtype: the rdata type desired
        @type rdtype: int or string
        @param covers: the covered type (defaults to None)
        @type covers: int or string
        """

        name = self._validate_name(name)
        if isinstance(rdtype, string_types):
            rdtype = dns.rdatatype.from_text(rdtype)
        if isinstance(covers, string_types):
            covers = dns.rdatatype.from_text(covers)
        node = self.get_node(name)
        if node is not None:
            node.delete_rdataset(self.rdclass, rdtype, covers)
            if len(node) == 0:
                self.delete_node(name) 

def get_rdataset(self, name, rdtype, covers=dns.rdatatype.NONE,
                     create=False):
        """Look for rdata with the specified name and type in the zone,
        and return an rdataset encapsulating it.

        The I{name}, I{rdtype}, and I{covers} parameters may be
        strings, in which case they will be converted to their proper
        type.

        The rdataset returned is not a copy; changes to it will change
        the zone.

        None is returned if the name or type are not found.
        Use L{find_rdataset} if you want to have KeyError raised instead.

        @param name: the owner name to look for
        @type name: DNS.name.Name object or string
        @param rdtype: the rdata type desired
        @type rdtype: int or string
        @param covers: the covered type (defaults to None)
        @type covers: int or string
        @param create: should the node and rdataset be created if they do not
        exist?
        @type create: bool
        @rtype: dns.rrset.RRset object
        """

        try:
            rdataset = self.find_rdataset(name, rdtype, covers, create)
        except KeyError:
            rdataset = None
        return rdataset 

def find_rdataset(self, name, rdtype, covers=dns.rdatatype.NONE,
                      create=False):
        """Look for rdata with the specified name and type in the zone,
        and return an rdataset encapsulating it.

        The I{name}, I{rdtype}, and I{covers} parameters may be
        strings, in which case they will be converted to their proper
        type.

        The rdataset returned is not a copy; changes to it will change
        the zone.

        KeyError is raised if the name or type are not found.
        Use L{get_rdataset} if you want to have None returned instead.

        @param name: the owner name to look for
        @type name: DNS.name.Name object or string
        @param rdtype: the rdata type desired
        @type rdtype: int or string
        @param covers: the covered type (defaults to None)
        @type covers: int or string
        @param create: should the node and rdataset be created if they do not
        exist?
        @type create: bool
        @raises KeyError: the node or rdata could not be found
        @rtype: dns.rrset.RRset object
        """

        name = self._validate_name(name)
        if isinstance(rdtype, string_types):
            rdtype = dns.rdatatype.from_text(rdtype)
        if isinstance(covers, string_types):
            covers = dns.rdatatype.from_text(covers)
        node = self.find_node(name, create)
        return node.find_rdataset(self.rdclass, rdtype, covers, create) 

def present(self, name, *args):
        """Require that an owner name (and optionally an rdata type,
        or specific rdataset) exists as a prerequisite to the
        execution of the update.  The first argument is always a name.
        The other arguments can be:

                - rdataset...

                - rdata...

                - rdtype, string..."""

        if isinstance(name, string_types):
            name = dns.name.from_text(name, None)
        if len(args) == 0:
            self.find_rrset(self.answer, name,
                            dns.rdataclass.ANY, dns.rdatatype.ANY,
                            dns.rdatatype.NONE, None,
                            True, True)
        elif isinstance(args[0], dns.rdataset.Rdataset) or \
            isinstance(args[0], dns.rdata.Rdata) or \
                len(args) > 1:
            if not isinstance(args[0], dns.rdataset.Rdataset):
                # Add a 0 TTL
                args = list(args)
                args.insert(0, 0)
            self._add(False, self.answer, name, *args)
        else:
            rdtype = args[0]
            if isinstance(rdtype, string_types):
                rdtype = dns.rdatatype.from_text(rdtype)
            self.find_rrset(self.answer, name,
                            dns.rdataclass.ANY, rdtype,
                            dns.rdatatype.NONE, None,
                            True, True) 

def replace(self, name, *args):
        """Replace records.  The first argument is always a name.  The other
        arguments can be:

                - rdataset...

                - ttl, rdata...

                - ttl, rdtype, string...

        Note that if you want to replace the entire node, you should do
        a delete of the name followed by one or more calls to add."""

        self._add(True, self.authority, name, *args) 

def add(self, name, *args):
        """Add records.  The first argument is always a name.  The other
        arguments can be:

                - rdataset...

                - ttl, rdata...

                - ttl, rdtype, string..."""
        self._add(False, self.authority, name, *args) 

def _add(self, replace, section, name, *args):
        """Add records.  The first argument is the replace mode.  If
        false, RRs are added to an existing RRset; if true, the RRset
        is replaced with the specified contents.  The second
        argument is the section to add to.  The third argument
        is always a name.  The other arguments can be:

                - rdataset...

                - ttl, rdata...

                - ttl, rdtype, string..."""

        if isinstance(name, string_types):
            name = dns.name.from_text(name, None)
        if isinstance(args[0], dns.rdataset.Rdataset):
            for rds in args:
                if replace:
                    self.delete(name, rds.rdtype)
                for rd in rds:
                    self._add_rr(name, rds.ttl, rd, section=section)
        else:
            args = list(args)
            ttl = int(args.pop(0))
            if isinstance(args[0], dns.rdata.Rdata):
                if replace:
                    self.delete(name, args[0].rdtype)
                for rd in args:
                    self._add_rr(name, ttl, rd, section=section)
            else:
                rdtype = args.pop(0)
                if isinstance(rdtype, string_types):
                    rdtype = dns.rdatatype.from_text(rdtype)
                if replace:
                    self.delete(name, rdtype)
                for s in args:
                    rd = dns.rdata.from_text(self.zone_rdclass, rdtype, s,
                                             self.origin)
                    self._add_rr(name, ttl, rd, section=section) 

def _add(self, replace, section, name, *args):
        """Add records.  The first argument is the replace mode.  If
        false, RRs are added to an existing RRset; if true, the RRset
        is replaced with the specified contents.  The second
        argument is the section to add to.  The third argument
        is always a name.  The other arguments can be:

                - rdataset...

                - ttl, rdata...

                - ttl, rdtype, string..."""

        if isinstance(name, string_types):
            name = dns.name.from_text(name, None)
        if isinstance(args[0], dns.rdataset.Rdataset):
            for rds in args:
                if replace:
                    self.delete(name, rds.rdtype)
                for rd in rds:
                    self._add_rr(name, rds.ttl, rd, section=section)
        else:
            args = list(args)
            ttl = int(args.pop(0))
            if isinstance(args[0], dns.rdata.Rdata):
                if replace:
                    self.delete(name, args[0].rdtype)
                for rd in args:
                    self._add_rr(name, ttl, rd, section=section)
            else:
                rdtype = args.pop(0)
                if isinstance(rdtype, string_types):
                    rdtype = dns.rdatatype.from_text(rdtype)
                if replace:
                    self.delete(name, rdtype)
                for s in args:
                    rd = dns.rdata.from_text(self.zone_rdclass, rdtype, s,
                                             self.origin)
                    self._add_rr(name, ttl, rd, section=section) 

def add(self, rd, ttl=None):
        """Add the specified rdata to the rdataset.

        If the optional I{ttl} parameter is supplied, then
        self.update_ttl(ttl) will be called prior to adding the rdata.

        @param rd: The rdata
        @type rd: dns.rdata.Rdata object
        @param ttl: The TTL
        @type ttl: int"""

        #
        # If we're adding a signature, do some special handling to
        # check that the signature covers the same type as the
        # other rdatas in this rdataset.  If this is the first rdata
        # in the set, initialize the covers field.
        #
        if self.rdclass != rd.rdclass or self.rdtype != rd.rdtype:
            raise IncompatibleTypes
        if not ttl is None:
            self.update_ttl(ttl)
        if self.rdtype == dns.rdatatype.RRSIG or \
           self.rdtype == dns.rdatatype.SIG:
            covers = rd.covers()
            if len(self) == 0 and self.covers == dns.rdatatype.NONE:
                self.covers = covers
            elif self.covers != covers:
                raise DifferingCovers
        if dns.rdatatype.is_singleton(rd.rdtype) and len(self) > 0:
            self.clear()
        super(Rdataset, self).add(rd)