"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')
