21.20. 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

New in version 3.7.


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


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


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 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(bytes_le=b'\x78\x56\x34\x12\x34\x12\x78\x56' +
UUID(fields=(0x12345678, 0x1234, 0x5678, 0x12, 0x34, 0x567812345678))

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:


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


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


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

The UUID as a 32-character hexadecimal string.


The UUID as a 128-bit integer.


The UUID as a URN as specified in RFC 4122.


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.


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


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

New in version 3.7.

The uuid module defines the following functions:


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).


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().


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


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


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


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 for NCS compatibility.


Specifies the UUID layout given in RFC 4122.


Reserved for Microsoft compatibility.


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()

>>> # make a UUID using an MD5 hash of a namespace UUID and a name
>>> uuid.uuid3(uuid.NAMESPACE_DNS, 'python.org')

>>> # make a random UUID
>>> uuid.uuid4()

>>> # make a UUID using a SHA-1 hash of a namespace UUID and a name
>>> uuid.uuid5(uuid.NAMESPACE_DNS, 'python.org')

>>> # 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)

>>> # get the raw 16 bytes of the UUID
>>> x.bytes

>>> # make a UUID from a 16-byte string
>>> uuid.UUID(bytes=x.bytes)