:mod:`uuid` --- UUID objects according to :rfc:`4122`
=====================================================
.. module:: uuid
:synopsis: UUID objects (universally unique identifiers) according to RFC 4122
.. moduleauthor:: Ka-Ping Yee <ping@zesty.ca>
.. sectionauthor:: George Yoshida <quiver@users.sourceforge.net>
**Source code:** :source:`Lib/uuid.py`
--------------
This module provides immutable :class:`UUID` objects (the :class:`UUID` class)
and the functions :func:`uuid1`, :func:`uuid3`, :func:`uuid4`, :func:`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 :func:`uuid1` or
:func:`uuid4`. Note that :func:`uuid1` may compromise privacy since it creates
a UUID containing the computer's network address. :func:`uuid4` creates a
random UUID.
Depending on support from the underlying platform, :func:`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 :class:`UUID` have an :attr:`is_safe` attribute
which relays any information about the UUID's safety, using this enumeration:
.. class:: SafeUUID
.. versionadded:: 3.7
.. attribute:: SafeUUID.safe
The UUID was generated by the platform in a multiprocessing-safe way.
.. attribute:: SafeUUID.unsafe
The UUID was not generated in a multiprocessing-safe way.
.. attribute:: SafeUUID.unknown
The platform does not provide information on whether the UUID was
generated safely or not.
.. class:: 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
:attr:`UUID.int` attributes. Comparison with a non-UUID object
raises a :exc:`TypeError`.
``str(uuid)`` returns a string in the form
``12345678-1234-5678-1234-567812345678`` where the 32 hexadecimal digits
represent the UUID.
:class:`UUID` instances have these read-only attributes:
.. attribute:: UUID.bytes
The UUID as a 16-byte string (containing the six integer fields in big-endian
byte order).
.. attribute:: UUID.bytes_le
The UUID as a 16-byte string (with *time_low*, *time_mid*, and *time_hi_version*
in little-endian byte order).
.. attribute:: 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 |
+==============================+===============================+
| :attr:`time_low` | the first 32 bits of the UUID |
+------------------------------+-------------------------------+
| :attr:`time_mid` | the next 16 bits of the UUID |
+------------------------------+-------------------------------+
| :attr:`time_hi_version` | the next 16 bits of the UUID |
+------------------------------+-------------------------------+
| :attr:`clock_seq_hi_variant` | the next 8 bits of the UUID |
+------------------------------+-------------------------------+
| :attr:`clock_seq_low` | the next 8 bits of the UUID |
+------------------------------+-------------------------------+
| :attr:`node` | the last 48 bits of the UUID |
+------------------------------+-------------------------------+
| :attr:`time` | the 60-bit timestamp |
+------------------------------+-------------------------------+
| :attr:`clock_seq` | the 14-bit sequence number |
+------------------------------+-------------------------------+
.. attribute:: UUID.hex
The UUID as a 32-character lowercase hexadecimal string.
.. attribute:: UUID.int
The UUID as a 128-bit integer.
.. attribute:: UUID.urn
The UUID as a URN as specified in :rfc:`4122`.
.. attribute:: UUID.variant
The UUID variant, which determines the internal layout of the UUID. This will be
one of the constants :const:`RESERVED_NCS`, :const:`RFC_4122`,
:const:`RESERVED_MICROSOFT`, or :const:`RESERVED_FUTURE`.
.. attribute:: UUID.version
The UUID version number (1 through 5, meaningful only when the variant is
:const:`RFC_4122`).
.. attribute:: UUID.is_safe
An enumeration of :class:`SafeUUID` which indicates whether the platform
generated the UUID in a multiprocessing-safe way.
.. versionadded:: 3.7
The :mod:`uuid` module defines the following functions:
.. function:: 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.
.. versionchanged:: 3.7
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.
.. index:: single: getnode
.. function:: uuid1(node=None, clock_seq=None)
Generate a UUID from a host ID, sequence number, and the current time. If *node*
is not given, :func:`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.
.. index:: single: uuid1
.. function:: 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).
.. index:: single: uuid3
.. function:: uuid4()
Generate a random UUID.
.. index:: single: uuid4
.. function:: 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).
.. index:: single: uuid5
The :mod:`uuid` module defines the following namespace identifiers for use with
:func:`uuid3` or :func:`uuid5`.
.. data:: NAMESPACE_DNS
When this namespace is specified, the *name* string is a fully qualified domain
name.
.. data:: NAMESPACE_URL
When this namespace is specified, the *name* string is a URL.
.. data:: NAMESPACE_OID
When this namespace is specified, the *name* string is an ISO OID.
.. data:: NAMESPACE_X500
When this namespace is specified, the *name* string is an X.500 DN in DER or a
text output format.
The :mod:`uuid` module defines the following constants for the possible values
of the :attr:`variant` attribute:
.. data:: RESERVED_NCS
Reserved for NCS compatibility.
.. data:: RFC_4122
Specifies the UUID layout given in :rfc:`4122`.
.. data:: RESERVED_MICROSOFT
Reserved for Microsoft compatibility.
.. data:: RESERVED_FUTURE
Reserved for future definition.
.. seealso::
: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.
.. _uuid-example:
Example
-------
Here are some examples of typical usage of the :mod:`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')
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