2018-04-01-UUID_6ba7b810-9dad-11d1-优快云博客

UUID

是通用唯一识别码（Universally Unique Identifier）的缩写

定义

UUID是由一组32位数的16进制数字所构成，是故UUID理论上的总数为16³²⁼²128，约等于3.4 x 10^38。

UUID的标准型式包含32个16进制数字，以连字号分为五段，形式为8-4-4-4-12的32个字符。示例：

550e8400-e29b-41d4-a716-446655440000


UUID Version 1：基于时间的UUID
基于时间的UUID通过计算当前时间戳、随机数和机器MAC地址得到。
UID Version 2：DCE安全的UUID
DCE（Distributed Computing Environment）安全的UUID和基于时间的UUID算法相同，但会把时间戳的前4位置换为POSIX的UID或GID。
UUID Version 3：基于名字的UUID（MD5）
基于名字的UUID通过计算名字和名字空间的MD5散列值得到。这个版本的UUID保证了：相同名字空间中不同名字生成的UUID的唯一性；
UUID Version 4：随机UUID
根据随机数，或者伪随机数生成UUID。这种UUID产生重复的概率是可以计算出来的，但随机的东西就像是买彩票：你指望它发财是不可能的，但狗屎运通常会在不经意中到来。
UUID Version 5：基于名字的UUID（SHA1）
和版本3的UUID算法类似，只是散列值计算使用SHA1（Secure Hash Algorithm 1）算法。

应用:

通常我们建议使用UUID来标识对象或持久化数据

使用

>>> import uuid
>>> uuid
<module 'uuid' from 'd:\\Downloads\\python\\Python3\\lib\\uuid.py'>
>>> name = 'test_name'
>>> namespace = uuid.NAMESPACE_URL
>>> namespace
UUID('6ba7b811-9dad-11d1-80b4-00c04fd430c8')
>>> print(uuid.uuid1())
be17e138-35bc-11e8-a550-a417313eaed6
>>> print(uuid.uuid3(namespace,name))
f15bb8f8-2f0c-3b7c-9ee7-79b874d9837b
>>> print(uuid.uuid4())
9de3ab8b-21a1-448e-be6a-4a3fb77a475e
>>> print(uuid.uuid5(namespace,name))
62740382-6394-5d1c-b9ef-d5a953ac1213

源码

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).
    if _uuid_generate_time and node is clock_seq is None:
        _buffer = ctypes.create_string_buffer(16)
        _uuid_generate_time(_buffer)
        return UUID(bytes=_buffer.raw)

    global _last_timestamp
    import time
    nanoseconds = int(time.time() * 1e9)
    # 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 = int(nanoseconds//100) + 0x01b21dd213814000L
    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.randrange(1<<14L) # instead of stable storage
    time_low = timestamp & 0xffffffffL
    time_mid = (timestamp >> 32L) & 0xffffL
    time_hi_version = (timestamp >> 48L) & 0x0fffL
    clock_seq_low = clock_seq & 0xffL
    clock_seq_hi_variant = (clock_seq >> 8L) & 0x3fL
    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 + name).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 + name).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')