When should I use uuid.uuid1() vs. uuid.uuid4() in python?
I understand the differences between the two from the docs. uuid1() :
Generate a UUID from a host ID, sequence number, and the current time uuid4() :
Generate a random UUID. So uuid1 uses machine/sequence/time info to generate a UUID. What are the pros and cons of using each? I know uuid1() can have privacy concerns, since it’s based off of machine-information. I wonder if there’s any more subtle when choosing one or the other. I just use uuid4() right now, since it’s a completely random UUID. But I wonder if I should be using uuid1 to lessen the risk of collisions. Basically, I’m looking for people’s tips for best-practices on using one vs. the other. Thanks!
Here is an alternative approach to UUID. Though the chance of collision is infinitesimal UUID doesn’t guarantee uniqueness. To guarantee the uniqueness you may want to use compound key as [
6 Answers 6
uuid1() is guaranteed to not produce any collisions (under the assumption you do not create too many of them at the same time). I wouldn’t use it if it’s important that there’s no connection between the uuid and the computer, as the mac address gets used to make it unique across computers.
You can create duplicates by creating more than 2 14 uuid1 in less than 100ns, but this is not a problem for most use cases.
uuid4() generates, as you said, a random UUID. The chance of a collision is really, really, really small. Small enough, that you shouldn’t worry about it. The problem is, that a bad random-number generator makes it more likely to have collisions.
This excellent answer by Bob Aman sums it up nicely. (I recommend reading the whole answer.)
Frankly, in a single application space without malicious actors, the extinction of all life on earth will occur long before you have a collision, even on a version 4 UUID, even if you’re generating quite a few UUIDs per second.
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.
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:
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 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('') 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:
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:
the first 32 bits of the UUID
the next 16 bits of the UUID
the next 16 bits of the UUID
the next 8 bits of the UUID
the next 8 bits of the UUID
the last 48 bits of the UUID
the 14-bit sequence number
The UUID as a 32-character lowercase 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.
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 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.
Changed in version 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.
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. 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.
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.
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('') >>> # 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')