# Source code for uuid

    r"""UUID objects (universally unique identifiers) according to RFC 4122.

    This module provides immutable UUID objects (class UUID) and the functions
    uuid1(), uuid3(), uuid4(), uuid5() for generating version 1, 3, 4, and 5
    UUIDs as specified in RFC 4122.

    If all you want is a unique ID, you should probably call uuid1() or uuid4().
    Note that uuid1() may compromise privacy since it creates a UUID containing
    the computer's network address.  uuid4() creates a random UUID.

    Typical usage:

        >>> import uuid

        # make a UUID based on the host ID and current time
        >>> uuid.uuid1()    # doctest: +SKIP
        UUID('a8098c1a-f86e-11da-bd1a-00112444be1e')

        # make a UUID using an MD5 hash of a namespace UUID and a name
        >>> uuid.uuid3(uuid.NAMESPACE_DNS, 'python.org')
        UUID('6fa459ea-ee8a-3ca4-894e-db77e160355e')

        # make a random UUID
        >>> uuid.uuid4()    # doctest: +SKIP
        UUID('16fd2706-8baf-433b-82eb-8c7fada847da')

        # make a UUID using a SHA-1 hash of a namespace UUID and a name
        >>> uuid.uuid5(uuid.NAMESPACE_DNS, 'python.org')
        UUID('886313e1-3b8a-5372-9b90-0c9aee199e5d')

        # make a UUID from a string of hex digits (braces and hyphens ignored)
        >>> x = uuid.UUID('{00010203-0405-0607-0809-0a0b0c0d0e0f}')

        # convert a UUID to a string of hex digits in standard form
        >>> str(x)
        '00010203-0405-0607-0809-0a0b0c0d0e0f'

        # get the raw 16 bytes of the UUID
        >>> x.bytes
        b'\x00\x01\x02\x03\x04\x05\x06\x07\x08\t\n\x0b\x0c\r\x0e\x0f'

        # make a UUID from a 16-byte string
        >>> uuid.UUID(bytes=x.bytes)
        UUID('00010203-0405-0607-0809-0a0b0c0d0e0f')
    """

    import os
    import platform
    import sys

    from enum import Enum

    __author__ = 'Ka-Ping Yee <ping@zesty.ca>'

    # The recognized platforms - known behaviors
    _AIX     = platform.system() == 'AIX'
    _DARWIN  = platform.system() == 'Darwin'
    _LINUX   = platform.system() == 'Linux'
    _WINDOWS = platform.system() == 'Windows'

    RESERVED_NCS, RFC_4122, RESERVED_MICROSOFT, RESERVED_FUTURE = [
        'reserved for NCS compatibility', 'specified in RFC 4122',
        'reserved for Microsoft compatibility', 'reserved for future definition']

    int_ = int      # The built-in int type
    bytes_ = bytes  # The built-in bytes type

    class SafeUUID(Enum):
        safe = 0
        unsafe = -1
        unknown = None

    class UUID:
        """Instances of the UUID class represent UUIDs as specified in RFC 4122.
        UUID objects are immutable, hashable, and usable as dictionary keys.
        Converting a UUID to a string with str() yields something in the form
        '12345678-1234-1234-1234-123456789abc'.  The UUID constructor accepts
        five possible forms: a similar string of hexadecimal digits, or a tuple
        of six integer fields (with 32-bit, 16-bit, 16-bit, 8-bit, 8-bit, and
        48-bit values respectively) as an argument named 'fields', or a string
        of 16 bytes (with all the integer fields in big-endian order) as an
        argument named 'bytes', or a string of 16 bytes (with the first three
        fields in little-endian order) as an argument named 'bytes_le', or a
        single 128-bit integer as an argument named 'int'.

        UUIDs have these read-only attributes:

            bytes       the UUID as a 16-byte string (containing the six
                        integer fields in big-endian byte order)

            bytes_le    the UUID as a 16-byte string (with time_low, time_mid,
                        and time_hi_version in little-endian byte order)

            fields      a tuple of the six integer fields of the UUID,
                        which are also available as six individual attributes
                        and two derived attributes:

                time_low                the first 32 bits of the UUID
                time_mid                the next 16 bits of the UUID
                time_hi_version         the next 16 bits of the UUID
                clock_seq_hi_variant    the next 8 bits of the UUID
                clock_seq_low           the next 8 bits of the UUID
                node                    the last 48 bits of the UUID

                time                    the 60-bit timestamp
                clock_seq               the 14-bit sequence number

            hex         the UUID as a 32-character hexadecimal string

            int         the UUID as a 128-bit integer

            urn         the UUID as a URN as specified in RFC 4122

            variant     the UUID variant (one of the constants RESERVED_NCS,
                        RFC_4122, RESERVED_MICROSOFT, or RESERVED_FUTURE)

            version     the UUID version number (1 through 5, meaningful only
                        when the variant is RFC_4122)

            is_safe     An enum indicating whether the UUID has been generated in
                        a way that is safe for multiprocessing applications, via
                        uuid_generate_time_safe(3).
        """

        __slots__ = ('int', 'is_safe', '__weakref__')

        def __init__(self, hex=None, bytes=None, bytes_le=None, fields=None,
                           int=None, version=None,
                           *, is_safe=SafeUUID.unknown):
            r"""Create a UUID from either a string of 32 hexadecimal digits,
            a string of 16 bytes as the 'bytes' argument, a string of 16 bytes
            in little-endian order as the 'bytes_le' argument, a tuple of six
            integers (32-bit time_low, 16-bit time_mid, 16-bit time_hi_version,
            8-bit clock_seq_hi_variant, 8-bit clock_seq_low, 48-bit node) as
            the 'fields' argument, or a single 128-bit integer as the 'int'
            argument.  When a string of hex digits is given, curly braces,
            hyphens, and a URN prefix are all optional.  For example, these
            expressions all yield the same UUID:

            UUID('{12345678-1234-5678-1234-567812345678}')
            UUID('12345678123456781234567812345678')
            UUID('urn:uuid:12345678-1234-5678-1234-567812345678')
            UUID(bytes='\x12\x34\x56\x78'*4)
            UUID(bytes_le='\x78\x56\x34\x12\x34\x12\x78\x56' +
                          '\x12\x34\x56\x78\x12\x34\x56\x78')
            UUID(fields=(0x12345678, 0x1234, 0x5678, 0x12, 0x34, 0x567812345678))
            UUID(int=0x12345678123456781234567812345678)

            Exactly one of 'hex', 'bytes', 'bytes_le', 'fields', or 'int' must
            be given.  The 'version' argument is optional; if given, the resulting
            UUID will have its variant and version set according to RFC 4122,
            overriding the given 'hex', 'bytes', 'bytes_le', 'fields', or 'int'.

            is_safe is an enum exposed as an attribute on the instance.  It
            indicates whether the UUID has been generated in a way that is safe
            for multiprocessing applications, via uuid_generate_time_safe(3).
            """

            if [hex, bytes, bytes_le, fields, int].count(None) != 4:
                raise TypeError('one of the hex, bytes, bytes_le, fields, '
                                'or int arguments must be given')
            if hex is not None:
                hex = hex.replace('urn:', '').replace('uuid:', '')
                hex = hex.strip('{}').replace('-', '')
                if len(hex) != 32:
                    raise ValueError('badly formed hexadecimal UUID string')
                int = int_(hex, 16)
            if bytes_le is not None:
                if len(bytes_le) != 16:
                    raise ValueError('bytes_le is not a 16-char string')
                bytes = (bytes_le[4-1::-1] + bytes_le[6-1:4-1:-1] +
                         bytes_le[8-1:6-1:-1] + bytes_le[8:])
            if bytes is not None:
                if len(bytes) != 16:
                    raise ValueError('bytes is not a 16-char string')
                assert isinstance(bytes, bytes_), repr(bytes)
                int = int_.from_bytes(bytes, byteorder='big')
            if fields is not None:
                if len(fields) != 6:
                    raise ValueError('fields is not a 6-tuple')
                (time_low, time_mid, time_hi_version,
                 clock_seq_hi_variant, clock_seq_low, node) = fields
                if not 0 <= time_low < 1<<32:
                    raise ValueError('field 1 out of range (need a 32-bit value)')
                if not 0 <= time_mid < 1<<16:
                    raise ValueError('field 2 out of range (need a 16-bit value)')
                if not 0 <= time_hi_version < 1<<16:
                    raise ValueError('field 3 out of range (need a 16-bit value)')
                if not 0 <= clock_seq_hi_variant < 1<<8:
                    raise ValueError('field 4 out of range (need an 8-bit value)')
                if not 0 <= clock_seq_low < 1<<8:
                    raise ValueError('field 5 out of range (need an 8-bit value)')
                if not 0 <= node < 1<<48:
                    raise ValueError('field 6 out of range (need a 48-bit value)')
                clock_seq = (clock_seq_hi_variant << 8) | clock_seq_low
                int = ((time_low << 96) | (time_mid << 80) |
                       (time_hi_version << 64) | (clock_seq << 48) | node)
            if int is not None:
                if not 0 <= int < 1<<128:
                    raise ValueError('int is out of range (need a 128-bit value)')
            if version is not None:
                if not 1 <= version <= 5:
                    raise ValueError('illegal version number')
                # Set the variant to RFC 4122.
                int &= ~(0xc000 << 48)
                int |= 0x8000 << 48
                # Set the version number.
                int &= ~(0xf000 << 64)
                int |= version << 76
            object.__setattr__(self, 'int', int)
            object.__setattr__(self, 'is_safe', is_safe)

        def __getstate__(self):
            d = {'int': self.int}
            if self.is_safe != SafeUUID.unknown:
                # is_safe is a SafeUUID instance.  Return just its value, so that
                # it can be un-pickled in older Python versions without SafeUUID.
                d['is_safe'] = self.is_safe.value
            return d

        def __setstate__(self, state):
            object.__setattr__(self, 'int', state['int'])
            # is_safe was added in 3.7; it is also omitted when it is "unknown"
            object.__setattr__(self, 'is_safe',
                               SafeUUID(state['is_safe'])
                               if 'is_safe' in state else SafeUUID.unknown)

        def __eq__(self, other):
            if isinstance(other, UUID):
                return self.int == other.int
            return NotImplemented

        # Q. What's the value of being able to sort UUIDs?
        # A. Use them as keys in a B-Tree or similar mapping.

        def __lt__(self, other):
            if isinstance(other, UUID):
                return self.int < other.int
            return NotImplemented

        def __gt__(self, other):
            if isinstance(other, UUID):
                return self.int > other.int
            return NotImplemented

        def __le__(self, other):
            if isinstance(other, UUID):
                return self.int <= other.int
            return NotImplemented

        def __ge__(self, other):
            if isinstance(other, UUID):
                return self.int >= other.int
            return NotImplemented

        def __hash__(self):
            return hash(self.int)

        def __int__(self):
            return self.int

        def __repr__(self):
            return '%s(%r)' % (self.__class__.__name__, str(self))

        def __setattr__(self, name, value):
            raise TypeError('UUID objects are immutable')

        def __str__(self):
            hex = '%032x' % self.int
            return '%s-%s-%s-%s-%s' % (
                hex[:8], hex[8:12], hex[12:16], hex[16:20], hex[20:])

        @property
        def bytes(self):
            return self.int.to_bytes(16, 'big')

        @property
        def bytes_le(self):
            bytes = self.bytes
            return (bytes[4-1::-1] + bytes[6-1:4-1:-1] + bytes[8-1:6-1:-1] +
                    bytes[8:])

        @property
        def fields(self):
            return (self.time_low, self.time_mid, self.time_hi_version,
                    self.clock_seq_hi_variant, self.clock_seq_low, self.node)

        @property
        def time_low(self):
            return self.int >> 96

        @property
        def time_mid(self):
            return (self.int >> 80) & 0xffff

        @property
        def time_hi_version(self):
            return (self.int >> 64) & 0xffff

        @property
        def clock_seq_hi_variant(self):
            return (self.int >> 56) & 0xff

        @property
        def clock_seq_low(self):
            return (self.int >> 48) & 0xff

        @property
        def time(self):
            return (((self.time_hi_version & 0x0fff) << 48) |
                    (self.time_mid << 32) | self.time_low)

        @property
        def clock_seq(self):
            return (((self.clock_seq_hi_variant & 0x3f) << 8) |
                    self.clock_seq_low)

        @property
        def node(self):
            return self.int & 0xffffffffffff

        @property
        def hex(self):
            return '%032x' % self.int

        @property
        def urn(self):
            return 'urn:uuid:' + str(self)

        @property
        def variant(self):
            if not self.int & (0x8000 << 48):
                return RESERVED_NCS
            elif not self.int & (0x4000 << 48):
                return RFC_4122
            elif not self.int & (0x2000 << 48):
                return RESERVED_MICROSOFT
            else:
                return RESERVED_FUTURE

        @property
        def version(self):
            # The version bits are only meaningful for RFC 4122 UUIDs.
            if self.variant == RFC_4122:
                return int((self.int >> 76) & 0xf)

    def _popen(command, *args):
        import os, shutil, subprocess
        executable = shutil.which(command)
        if executable is None:
            path = os.pathsep.join(('/sbin', '/usr/sbin'))
            executable = shutil.which(command, path=path)
            if executable is None:
                return None
        # LC_ALL=C to ensure English output, stderr=DEVNULL to prevent output
        # on stderr (Note: we don't have an example where the words we search
        # for are actually localized, but in theory some system could do so.)
        env = dict(os.environ)
        env['LC_ALL'] = 'C'
        proc = subprocess.Popen((executable,) + args,
                                stdout=subprocess.PIPE,
                                stderr=subprocess.DEVNULL,
                                env=env)
        return proc

    # For MAC (a.k.a. IEEE 802, or EUI-48) addresses, the second least significant
    # bit of the first octet signifies whether the MAC address is universally (0)
    # or locally (1) administered.  Network cards from hardware manufacturers will
    # always be universally administered to guarantee global uniqueness of the MAC
    # address, but any particular machine may have other interfaces which are
    # locally administered.  An example of the latter is the bridge interface to
    # the Touch Bar on MacBook Pros.
    #
    # This bit works out to be the 42nd bit counting from 1 being the least
    # significant, or 1<<41.  We'll prefer universally administered MAC addresses
    # over locally administered ones since the former are globally unique, but
    # we'll return the first of the latter found if that's all the machine has.
    #
    # See https://en.wikipedia.org/wiki/MAC_address#Universal_vs._local

    def _is_universal(mac):
        return not (mac & (1 << 41))

    def _find_mac(command, args, hw_identifiers, get_index):
        first_local_mac = None
        try:
            proc = _popen(command, *args.split())
            if not proc:
                return None
            with proc:
                for line in proc.stdout:
                    words = line.lower().rstrip().split()
                    for i in range(len(words)):
                        if words[i] in hw_identifiers:
                            try:
                                word = words[get_index(i)]
                                mac = int(word.replace(b':', b''), 16)
                                if _is_universal(mac):
                                    return mac
                                first_local_mac = first_local_mac or mac
                            except (ValueError, IndexError):
                                # Virtual interfaces, such as those provided by
                                # VPNs, do not have a colon-delimited MAC address
                                # as expected, but a 16-byte HWAddr separated by
                                # dashes. These should be ignored in favor of a
                                # real MAC address
                                pass
        except OSError:
            pass
        return first_local_mac or None

    def _ifconfig_getnode():
        """Get the hardware address on Unix by running ifconfig."""
        # This works on Linux ('' or '-a'), Tru64 ('-av'), but not all Unixes.
        keywords = (b'hwaddr', b'ether', b'address:', b'lladdr')
        for args in ('', '-a', '-av'):
            mac = _find_mac('ifconfig', args, keywords, lambda i: i+1)
            if mac:
                return mac
            return None

    def _ip_getnode():
        """Get the hardware address on Unix by running ip."""
        # This works on Linux with iproute2.
        mac = _find_mac('ip', 'link', [b'link/ether'], lambda i: i+1)
        if mac:
            return mac
        return None

    def _arp_getnode():
        """Get the hardware address on Unix by running arp."""
        import os, socket
        try:
            ip_addr = socket.gethostbyname(socket.gethostname())
        except OSError:
            return None

        # Try getting the MAC addr from arp based on our IP address (Solaris).
        mac = _find_mac('arp', '-an', [os.fsencode(ip_addr)], lambda i: -1)
        if mac:
            return mac

        # This works on OpenBSD
        mac = _find_mac('arp', '-an', [os.fsencode(ip_addr)], lambda i: i+1)
        if mac:
            return mac

        # This works on Linux, FreeBSD and NetBSD
        mac = _find_mac('arp', '-an', [os.fsencode('(%s)' % ip_addr)],
                        lambda i: i+2)
        # Return None instead of 0.
        if mac:
            return mac
        return None

    def _lanscan_getnode():
        """Get the hardware address on Unix by running lanscan."""
        # This might work on HP-UX.
        return _find_mac('lanscan', '-ai', [b'lan0'], lambda i: 0)

    def _netstat_getnode():
        """Get the hardware address on Unix by running netstat."""
        # This might work on AIX, Tru64 UNIX.
        first_local_mac = None
        try:
            proc = _popen('netstat', '-ia')
            if not proc:
                return None
            with proc:
                words = proc.stdout.readline().rstrip().split()
                try:
                    i = words.index(b'Address')
                except ValueError:
                    return None
                for line in proc.stdout:
                    try:
                        words = line.rstrip().split()
                        word = words[i]
                        if len(word) == 17 and word.count(b':') == 5:
                            mac = int(word.replace(b':', b''), 16)
                            if _is_universal(mac):
                                return mac
                            first_local_mac = first_local_mac or mac
                    except (ValueError, IndexError):
                        pass
        except OSError:
            pass
        return first_local_mac or None

    def _ipconfig_getnode():
        """Get the hardware address on Windows by running ipconfig.exe."""
        import os, re, subprocess
        first_local_mac = None
        dirs = ['', r'c:\windows\system32', r'c:\winnt\system32']
        try:
            import ctypes
            buffer = ctypes.create_string_buffer(300)
            ctypes.windll.kernel32.GetSystemDirectoryA(buffer, 300)
            dirs.insert(0, buffer.value.decode('mbcs'))
        except:
            pass
        for dir in dirs:
            try:
                proc = subprocess.Popen([os.path.join(dir, 'ipconfig'), '/all'],
                                        stdout=subprocess.PIPE,
                                        encoding="oem")
            except OSError:
                continue
            with proc:
                for line in proc.stdout:
                    value = line.split(':')[-1].strip().lower()
                    if re.fullmatch('(?:[0-9a-f][0-9a-f]-){5}[0-9a-f][0-9a-f]', value):
                        mac = int(value.replace('-', ''), 16)
                        if _is_universal(mac):
                            return mac
                        first_local_mac = first_local_mac or mac
        return first_local_mac or None

    def _netbios_getnode():
        """Get the hardware address on Windows using NetBIOS calls.
        See http://support.microsoft.com/kb/118623 for details."""
        import win32wnet, netbios
        first_local_mac = None
        ncb = netbios.NCB()
        ncb.Command = netbios.NCBENUM
        ncb.Buffer = adapters = netbios.LANA_ENUM()
        adapters._pack()
        if win32wnet.Netbios(ncb) != 0:
            return None
        adapters._unpack()
        for i in range(adapters.length):
            ncb.Reset()
            ncb.Command = netbios.NCBRESET
            ncb.Lana_num = ord(adapters.lana[i])
            if win32wnet.Netbios(ncb) != 0:
                continue
            ncb.Reset()
            ncb.Command = netbios.NCBASTAT
            ncb.Lana_num = ord(adapters.lana[i])
            ncb.Callname = '*'.ljust(16)
            ncb.Buffer = status = netbios.ADAPTER_STATUS()
            if win32wnet.Netbios(ncb) != 0:
                continue
            status._unpack()
            bytes = status.adapter_address[:6]
            if len(bytes) != 6:
                continue
            mac = int.from_bytes(bytes, 'big')
            if _is_universal(mac):
                return mac
            first_local_mac = first_local_mac or mac
        return first_local_mac or None

    _generate_time_safe = _UuidCreate = None
    _has_uuid_generate_time_safe = None

    # Import optional C extension at toplevel, to help disabling it when testing
    try:
        import _uuid
    except ImportError:
        _uuid = None

    def _load_system_functions():
        """
        Try to load platform-specific functions for generating uuids.
        """
        global _generate_time_safe, _UuidCreate, _has_uuid_generate_time_safe

        if _has_uuid_generate_time_safe is not None:
            return

        _has_uuid_generate_time_safe = False

        if sys.platform == "darwin" and int(os.uname().release.split('.')[0]) < 9:
            # The uuid_generate_* functions are broken on MacOS X 10.5, as noted
            # in issue #8621 the function generates the same sequence of values
            # in the parent process and all children created using fork (unless
            # those children use exec as well).
            #
            # Assume that the uuid_generate functions are broken from 10.5 onward,
            # the test can be adjusted when a later version is fixed.
            pass
        elif _uuid is not None:
            _generate_time_safe = _uuid.generate_time_safe
            _has_uuid_generate_time_safe = _uuid.has_uuid_generate_time_safe
            return

        try:
            # If we couldn't find an extension module, try ctypes to find
            # system routines for UUID generation.
            # Thanks to Thomas Heller for ctypes and for his help with its use here.
            import ctypes
            import ctypes.util

            # The uuid_generate_* routines are provided by libuuid on at least
            # Linux and FreeBSD, and provided by libc on Mac OS X.
            _libnames = ['uuid']
            if not sys.platform.startswith('win'):
                _libnames.append('c')
            for libname in _libnames:
                try:
                    lib = ctypes.CDLL(ctypes.util.find_library(libname))
                except Exception:                           # pragma: nocover
                    continue
                # Try to find the safe variety first.
                if hasattr(lib, 'uuid_generate_time_safe'):
                    _uuid_generate_time_safe = lib.uuid_generate_time_safe
                    # int uuid_generate_time_safe(uuid_t out);
                    def _generate_time_safe():
                        _buffer = ctypes.create_string_buffer(16)
                        res = _uuid_generate_time_safe(_buffer)
                        return bytes(_buffer.raw), res
                    _has_uuid_generate_time_safe = True
                    break

                elif hasattr(lib, 'uuid_generate_time'):    # pragma: nocover
                    _uuid_generate_time = lib.uuid_generate_time
                    # void uuid_generate_time(uuid_t out);
                    _uuid_generate_time.restype = None
                    def _generate_time_safe():
                        _buffer = ctypes.create_string_buffer(16)
                        _uuid_generate_time(_buffer)
                        return bytes(_buffer.raw), None
                    break

            # On Windows prior to 2000, UuidCreate gives a UUID containing the
            # hardware address.  On Windows 2000 and later, UuidCreate makes a
            # random UUID and UuidCreateSequential gives a UUID containing the
            # hardware address.  These routines are provided by the RPC runtime.
            # NOTE:  at least on Tim's WinXP Pro SP2 desktop box, while the last
            # 6 bytes returned by UuidCreateSequential are fixed, they don't appear
            # to bear any relationship to the MAC address of any network device
            # on the box.
            try:
                lib = ctypes.windll.rpcrt4
            except:
                lib = None
            _UuidCreate = getattr(lib, 'UuidCreateSequential',
                                  getattr(lib, 'UuidCreate', None))

        except Exception as exc:
            import warnings
            warnings.warn(f"Could not find fallback ctypes uuid functions: {exc}",
                          ImportWarning)

    def _unix_getnode():
        """Get the hardware address on Unix using the _uuid extension module
        or ctypes."""
        _load_system_functions()
        uuid_time, _ = _generate_time_safe()
        return UUID(bytes=uuid_time).node

    def _windll_getnode():
        """Get the hardware address on Windows using ctypes."""
        import ctypes
        _load_system_functions()
        _buffer = ctypes.create_string_buffer(16)
        if _UuidCreate(_buffer) == 0:
            return UUID(bytes=bytes_(_buffer.raw)).node

    def _random_getnode():
        """Get a random node ID."""
        # RFC 4122, $4.1.6 says "For systems with no IEEE address, a randomly or
        # pseudo-randomly generated value may be used; see Section 4.5.  The
        # multicast bit must be set in such addresses, in order that they will
        # never conflict with addresses obtained from network cards."
        #
        # The "multicast bit" of a MAC address is defined to be "the least
        # significant bit of the first octet".  This works out to be the 41st bit
        # counting from 1 being the least significant bit, or 1<<40.
        #
        # See https://en.wikipedia.org/wiki/MAC_address#Unicast_vs._multicast
        import random
        return random.getrandbits(48) | (1 << 40)

    # _OS_GETTERS, when known, are targeted for a specific OS or platform.
    # The order is by 'common practice' on the specified platform.
    # Note: 'posix' and 'windows' _OS_GETTERS are prefixed by a dll/dlload() method
    # which, when successful, means none of these "external" methods are called.
    # _GETTERS is (also) used by test_uuid.py to SkipUnless(), e.g.,
    #     @unittest.skipUnless(_uuid._ifconfig_getnode in _uuid._GETTERS, ...)
    if _LINUX:
        _OS_GETTERS = [_ip_getnode, _ifconfig_getnode]
    elif _DARWIN:
        _OS_GETTERS = [_ifconfig_getnode, _arp_getnode, _netstat_getnode]
    elif _WINDOWS:
        _OS_GETTERS = [_netbios_getnode, _ipconfig_getnode]
    elif _AIX:
        _OS_GETTERS = [_netstat_getnode]
    else:
        _OS_GETTERS = [_ifconfig_getnode, _ip_getnode, _arp_getnode,
                       _netstat_getnode, _lanscan_getnode]
    if os.name == 'posix':
        _GETTERS = [_unix_getnode] + _OS_GETTERS
    elif os.name == 'nt':
        _GETTERS = [_windll_getnode] + _OS_GETTERS
    else:
        _GETTERS = _OS_GETTERS

    _node = None

    def getnode(*, getters=None):
        """Get the hardware address as a 48-bit positive integer.

        The first time this runs, it may launch a separate program, which could
        be quite slow.  If all attempts to obtain the hardware address fail, we
        choose a random 48-bit number with its eighth bit set to 1 as recommended
        in RFC 4122.
        """
        global _node
        if _node is not None:
            return _node

        for getter in _GETTERS + [_random_getnode]:
            try:
                _node = getter()
            except:
                continue
            if (_node is not None) and (0 <= _node < (1 << 48)):
                return _node
        assert False, '_random_getnode() returned invalid value: {}'.format(_node)

    _last_timestamp = None

    def uuid1(node=None, clock_seq=None):
        """Generate a UUID from a host ID, sequence number, and the current time.
        If 'node' is not given, getnode() is used to obtain the hardware
        address.  If 'clock_seq' is given, it is used as the sequence number;
        otherwise a random 14-bit sequence number is chosen."""

        # When the system provides a version-1 UUID generator, use it (but don't
        # use UuidCreate here because its UUIDs don't conform to RFC 4122).
        _load_system_functions()
        if _generate_time_safe is not None and node is clock_seq is None:
            uuid_time, safely_generated = _generate_time_safe()
            try:
                is_safe = SafeUUID(safely_generated)
            except ValueError:
                is_safe = SafeUUID.unknown
            return UUID(bytes=uuid_time, is_safe=is_safe)

        global _last_timestamp
        import time
        nanoseconds = time.time_ns()
        # 0x01b21dd213814000 is the number of 100-ns intervals between the
        # UUID epoch 1582-10-15 00:00:00 and the Unix epoch 1970-01-01 00:00:00.
        timestamp = nanoseconds // 100 + 0x01b21dd213814000
        if _last_timestamp is not None and timestamp <= _last_timestamp:
            timestamp = _last_timestamp + 1
        _last_timestamp = timestamp
        if clock_seq is None:
            import random
            clock_seq = random.getrandbits(14) # instead of stable storage
        time_low = timestamp & 0xffffffff
        time_mid = (timestamp >> 32) & 0xffff
        time_hi_version = (timestamp >> 48) & 0x0fff
        clock_seq_low = clock_seq & 0xff
        clock_seq_hi_variant = (clock_seq >> 8) & 0x3f
        if node is None:
            node = getnode()
        return UUID(fields=(time_low, time_mid, time_hi_version,
                            clock_seq_hi_variant, clock_seq_low, node), version=1)

    def uuid3(namespace, name):
        """Generate a UUID from the MD5 hash of a namespace UUID and a name."""
        from hashlib import md5
        hash = md5(namespace.bytes + bytes(name, "utf-8")).digest()
        return UUID(bytes=hash[:16], version=3)

    def uuid4():
        """Generate a random UUID."""
        return UUID(bytes=os.urandom(16), version=4)

    def uuid5(namespace, name):
        """Generate a UUID from the SHA-1 hash of a namespace UUID and a name."""
        from hashlib import sha1
        hash = sha1(namespace.bytes + bytes(name, "utf-8")).digest()
        return UUID(bytes=hash[:16], version=5)

    # The following standard UUIDs are for use with uuid3() or uuid5().

    NAMESPACE_DNS = UUID('6ba7b810-9dad-11d1-80b4-00c04fd430c8')
    NAMESPACE_URL = UUID('6ba7b811-9dad-11d1-80b4-00c04fd430c8')
    NAMESPACE_OID = UUID('6ba7b812-9dad-11d1-80b4-00c04fd430c8')
    NAMESPACE_X500 = UUID('6ba7b814-9dad-11d1-80b4-00c04fd430c8')