snowflake 0.0.2

Simple persistent unique IDs.

I’ve often found myself needing to have a per-machine unique identifier, but actually getting one of these is harder than it should be. You can’t just use the MAC address, since those aren’t guaranteed to be unique, especially when you’re working with a batch of cheap embedded devices. While not rocket science, it’s also not trivial to get the MAC address of a box sometimes: which interface to use? What if you change network cards? What if you have to spoof a MAC address? POSIX specifies gethostid(1), but on Linux the man page notes under “Bugs” that “It is impossible to ensure that the identifier is globally unique.” Indeed, my laptop and my work computer have the same hostid value.

Snowflake is a trivial wrapper around Python’s uuid library to create a persistent, per-machine UUID (called a ‘snowflake’) and give you a nice API to mess with it. Usage is simple:

>>> import snowflake
>>> snowflake.snowflake()
'7232c1c3-f6d1-4aec-bedd-c7e4c10dc8d3'

There’s also a script that can be run from the command line:

$ snowflake
7232c1c3-f6d1-4aec-bedd-c7e4c10dc8d3

Installation and Setup

To generate a machine’s snowflake ID, just install snowflake:

$ pip install snowflake

Or from source:

$ python setup.py install

The machine’s snowflake is saved in /etc/snowflake during installation. Any user can read this file, but only users with root access can modify it. You can also generate other snowflakes in other locations, so each user (or application) can make their own snowflakes.

Of course, you can do all this in Python too:

>>> import snowflake
>>> snowflake.make_snowflake(snowflake_file='foo')
ee2b1891-ccd3-4a23-9246-4ce40d20e740
>>> snowflake.snowflake(snowflake_file='foo')
ee2b1891-ccd3-4a23-9246-4ce40d20e740

Limitations

Right now, snowflake only works on Unix-y systems.

License

Copyright (c) 2012, Shaddi Hasan All rights reserved.

Redistribution and use in source and binary forms, with or without modification, are permitted provided that the following conditions are met:

1. Redistributions of source code must retain the above copyright notice, this list of conditions and the following disclaimer.

2. Redistributions in binary form must reproduce the above copyright notice, this list of conditions and the following disclaimer in the documentation and/or other materials provided with the distribution.

THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS “AS IS” AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT OWNER OR CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.