A ULID is a universally unique lexicographically sortable identifier. It is

• 128-bit compatible with UUID
• 1.21e+24 unique ULIDs per millisecond
• Lexicographically sortable!
• Canonically encoded as a 26 character string, as opposed to the 36 character UUID
• Uses Crockford's base32 for better efficiency and readability (5 bits per character)
• Case insensitive
• No special characters (URL safe)

In general the structure of a ULID is as follows:

 01AN4Z07BY      79KA1307SR9X4MV3
|----------|    |----------------|
 Timestamp          Randomness
   48bits             80bits

For more information have a look at the original specification.

Installation

Use pip to install the library

$ pip install python-ulid

to include Pydantic support install the optional dependency like so

$ pip install python-ulid[pydantic]

Basic Usage

Create a new ULID object from the current timestamp

>>> from ulid import ULID
>>> ULID()
ULID(01E75HZVW36EAZKMF1W7XNMSB4)

or use one of the named constructors

>>> import time, datetime
>>> ULID.from_timestamp(time.time())
ULID(01E75J1MKKWMGG0N5MBHFMRC84)
>>> ULID.from_datetime(datetime.datetime.now())
ULID(01E75J2XBK390V2XRH44EHC10X)

There are several options for encoding the ULID object (e.g. string, hex, int, bytes, UUID):

>>> str(ulid)
'01BTGNYV6HRNK8K8VKZASZCFPE'
>>> ulid.hex
'015ea15f6cd1c56689a373fab3f63ece'
>>> int(ulid)
1820576928786795198723644692628913870
>>> bytes(ulid)
b'\x01^\xa1_l\xd1\xc5f\x89\xa3s\xfa\xb3\xf6>\xce'
>>> ulid.to_uuid()
UUID('015ea15f-6cd1-c566-89a3-73fab3f63ece')

It is also possible to directly access the timestamp component of a ULID, either in UNIX epoch or as datetime.datetime

>>> ulid.timestamp
1505945939.153
>>> ulid.datetime
datetime.datetime(2017, 9, 20, 22, 18, 59, 153000, tzinfo=datetime.timezone.utc)

Pydantic integration

The ULID class can be directly used for the popular data validation library Pydantic like so

from pydantic import BaseModel
from ulid import ULID


class Model(BaseModel):
  ulid: ULID

model = Model(ulid="DX89370400440532013000")  # OK
model = Model(ulid="not-a-ulid")  # Raises ValidationError

Command line interface

The package comes with a CLI interface that can be invoked either by the script name ulid or as python module python -m ulid. The CLI allows you to generate, inspect and convert ULIDs, e.g.

$ ulid build
01HASFKBN8SKZTSVVS03K5AMMS

$ ulid build --from-datetime=2023-09-23T10:20:30
01HB0J0F5GCKEXNSWVAD5PEAC1

$ ulid show 01HASFKBN8SKZTSVVS03K5AMMS
ULID:      01HASFKBN8SKZTSVVS03K5AMMS
Hex:       018ab2f9aea8ccffacef7900e6555299
Int:       2049395013039097460549394558635823769
Timestamp: 1695219822.248
Datetime:  2023-09-20 14:23:42.248000+00:00

There are several flags to select specific output formats for the show command, e.g.

$ ulid show --datetime 01HASFKBN8SKZTSVVS03K5AMMS
2023-09-20 14:23:42.248000+00:00

The special character - allows to read values from stdin so that they can be piped. E.g.

$ echo 01HASFKBN8SKZTSVVS03K5AMMS | ulid show --uuid -
018ab2f9-aea8-4cff-acef-7900e6555299

$ date --iso-8601 | python -m ulid build --from-datetime -
01HAT9PVR02T3S13XB48S7GEHE

For a full overview of flags for the build and show commands use the --help option (e.g. ulid show --help).

Other implementations

• ahawker/ulid
• valohai/ulid2
• mdipierro/ulid
• oklog/ulid
• ulid/javascript
• RobThree/NUlid
• imdario/go-ulid