# 21.20. `uuid` — UUID objects according to RFC 4122

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.``UUID`(hex=None, bytes=None, bytes_le=None, fields=None, int=None, version=None)

  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=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.

`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`

  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

`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 integer 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`).

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 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.

`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.

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.

## 21.20.1. Example

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')