# `uuid` --- UUID objects according to RFC 4122

Source code: Lib/uuid.py

This module provides immutable `UUID` objects (the `UUID` class) 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.

Depending on support from the underlying platform, `uuid1()` may or may not return a "safe" UUID. A safe UUID is one which is generated using synchronization methods that ensure no two processes can obtain the same UUID. All instances of `UUID` have an `is_safe` attribute which relays any information about the UUID's safety, using this enumeration:

class `uuid.``SafeUUID`

  3.7 版新加入.

  `safe`

    The UUID was generated by the platform in a multiprocessing-safe way.

  `unsafe`

    The UUID was not generated in a multiprocessing-safe way.

  `unknown`

    The platform does not provide information on whether the UUID was generated safely or not.

class `uuid.``UUID`(hex=None, bytes=None, bytes_le=None, fields=None, int=None, version=None, *, is_safe=SafeUUID.unknown)

  Create a UUID from either a string of 32 hexadecimal digits, a string of 16 bytes in big-endian order 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=b'\x12\x34\x56\x78'*4)
      UUID(bytes_le=b'\x78\x56\x34\x12\x34\x12\x78\x56' +
                    b'\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 number set according to RFC 4122, overriding bits in the given hex, bytes, bytes_le, fields, or int.

  Comparison of UUID objects are made by way of comparing their `UUID.int` attributes. Comparison with a non-UUID object raises a `TypeError`.

  `str(uuid)` returns a string in the form `12345678-1234-5678-1234-567812345678` where the 32 hexadecimal digits represent the UUID.

`UUID` instances have these read-only attributes:

`UUID.``bytes`

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

`UUID.``bytes_le`

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

`UUID.``fields`

  以元组形式存放的UUID的6个整数域，有六个单独的属性和两个派生属性：

  域 | 意义
  --- | ---
  `time_low` | UUID的前32位
  `time_mid` | 接前一域的16位
  `time_hi_version` | 接前一域的16位
  `clock_seq_hi_variant` | 接前一域的8位
  `clock_seq_low` | 接前一域的8位
  `node` | UUID的最后48位
  `time` | UUID的总长60位的时间戳
  `clock_seq` | 14位的序列号

`UUID.``hex`

  The UUID as a 32-character hexadecimal string.

`UUID.``int`

  The UUID as a 128-bit integer.

`UUID.``urn`

  The UUID as a URN as specified in RFC 4122.

`UUID.``variant`

  The UUID variant, which determines the internal layout of the UUID. This will be one of the constants `RESERVED_NCS`, `RFC_4122`, `RESERVED_MICROSOFT`, or `RESERVED_FUTURE`.

`UUID.``version`

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

`UUID.``is_safe`

  An enumeration of `SafeUUID` which indicates whether the platform generated the UUID in a multiprocessing-safe way.

  3.7 版新加入.

The `uuid` module defines the following functions:

`uuid.``getnode`()

  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 the multicast bit (least significant bit of the first octet) set to 1 as recommended in RFC 4122. "Hardware address" means the MAC address of a network interface. On a machine with multiple network interfaces, universally administered MAC addresses (i.e. where the second least significant bit of the first octet is unset) will be preferred over locally administered MAC addresses, but with no other ordering guarantees.

  3.7 版更變: Universally administered MAC addresses are preferred over locally administered MAC addresses, since the former are guaranteed to be globally unique, while the latter are not.

`uuid.``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.

`uuid.``uuid3`(namespace, name)

  Generate a UUID based on the MD5 hash of a namespace identifier (which is a UUID) and a name (which is a string).

`uuid.``uuid4`()

  Generate a random UUID.

`uuid.``uuid5`(namespace, name)

  Generate a UUID based on the SHA-1 hash of a namespace identifier (which is a UUID) and a name (which is a string).

The `uuid` module defines the following namespace identifiers for use with `uuid3()` or `uuid5()`.

`uuid.``NAMESPACE_DNS`

  When this namespace is specified, the name string is a fully-qualified domain name.

`uuid.``NAMESPACE_URL`

  When this namespace is specified, the name string is a URL.

`uuid.``NAMESPACE_OID`

  When this namespace is specified, the name string is an ISO OID.

`uuid.``NAMESPACE_X500`

  When this namespace is specified, the name string is an X.500 DN in DER or a text output format.

The `uuid` module defines the following constants for the possible values of the `variant` attribute:

`uuid.``RESERVED_NCS`

  Reserved for NCS compatibility.

`uuid.``RFC_4122`

  Specifies the UUID layout given in RFC 4122.

`uuid.``RESERVED_MICROSOFT`

  Reserved for Microsoft compatibility.

`uuid.``RESERVED_FUTURE`

  Reserved for future definition.

也參考

RFC 4122 - A Universally Unique IDentifier (UUID) URN Namespace

  This specification defines a Uniform Resource Name namespace for UUIDs, the internal format of UUIDs, and methods of generating UUIDs.

## 示例

Here are some examples of typical usage of the `uuid` module:

    >>> import uuid

    >>> # make a UUID based on the host ID and current time
    >>> uuid.uuid1()
    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()
    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')