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

New in version 2.5.

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.

class `UUID`( | [hex[, bytes[, bytes_le[, fields[, int[, version]]]]]])

  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 number set according to RFC 4122, overriding bits in the given hex, bytes, bytes_le, fields, or int.

`UUID` instances 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:

  Field | Meaning
  --- | ---
  `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, which determines the internal layout of the UUID. This will be one of the integer 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`).

The `uuid` module defines the following functions:

`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 its eighth bit set to 1 as recommended in RFC 4122. "Hardware address" means the MAC address of a network interface, and on a machine with multiple network interfaces the MAC address of any one of them may be returned.

`uuid1`( | [node[, clock_seq]])

  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.

`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).

`uuid4`( | )

  Generate a random 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()`.

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

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

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

`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:

`RESERVED_NCS`
  Reserved for NCS compatibility.

`RFC_4122`
  Specifies the UUID layout given in RFC 4122.

`RESERVED_MICROSOFT`
  Reserved for Microsoft compatibility.

`RESERVED_FUTURE`
  Reserved for future definition.

See Also:

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.