Python 中的 UUID

python 中的 uuid
代码参考 cpython/Lib/uuid.py
版本 3.7

什么是 UUID

UUID 的全称是 Universal Unique Identifier，中文名是 通用唯一标识符；
wikipedia 上 UUID 的定义是

a 128-bit number used to identify information in computer systems

UUID 需要满足两个条件：

1. 128 bit
2. 具有标识别计算机系统的能力

UUID 的规则

格式

1. 将 16 个 8 位字节表示成 32 个十六进制数
2. 按照 8-4-4-4-12 的格式加上 4 个连字符 “-‘

   版本

   UUID 应该是下面的这种格式

xxxxxxxx-xxxx-Mxxx-Nxxx-xxxxxxxxxxxx

其中 M 开始的 4 位表示版本，N 开始的 4 位表示变种

Name                        Length(bytes)    Length(hex digits)                       Contents

time_low                         4                             8                  integer giving the low 32 bits of the time
time_mid                         2                             4                  integer giving the middle 16 bits of the time|
time_hi_and_version      2                              4                  4-bit “version” in the most significant bits,                                                                                               followed by the high 12 bits of the time
clock_seq_hi_and           2                             4                  1-3 bit “variant” in the most significant bits,  _resclock_seq_low                                                             followed by the 13-15 bit clock sequence|
node                               6                             12                  the 48-bit node id

Nil UUID

Version 1(date-time and MAC address)

Version 2 (date-time and MAC address, DCE security version)

Versions 3 and 5 (namespace name-based)

Version 4 (random)

UUID 在 python 中的实现

Version2 实际应用的比较少，python 中没有实现；
UUID 的实现就是按照规则将代码写出来，但是 UUID 这个类的初始化与获得机器信息的代码还是可以看看的

class UUID

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).
    """

    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
        self.__dict__['int'] = int
        self.__dict__['is_safe'] = is_safe

    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)

getnode

getnode 区别了 windows 与 unix
windows 的时候会从 windll、netbios 、ipconfig 中获取机器信息
uinx 的时候会从 ifconfig、ip、arp、lanscan、netstat 中获取机器信息
如果都失败了就会生成一个随机的 48 bit 的数字并将第八位至为 1

def getnode(*, getters=None):
    global _node
    if _node is not None:
        return _node

    if sys.platform == 'win32':
        getters = _NODE_GETTERS_WIN32
    else:
        getters = _NODE_GETTERS_UNIX

    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)

_popen

为了执行 ifconfig 等命令
python 中写了一个 _popen 的函数来完成命令的执行

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
    env = dict(os.environ)
    env['LC_ALL'] = 'C'
    proc = subprocess.Popen((executable,) + args,
                            stdout=subprocess.PIPE,
                            stderr=subprocess.DEVNULL,
                            env=env)
    return proc

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