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Can I use that code?

Software Licences as a User

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About Me

Holly Becker
Software Developer
Open source fan
Likes books, board games, birdwatching
hollybecker.net

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IANAL

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It's complicated!

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What is a licence?

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What is a software licence?

For software only!

For other creative works use Creative Commons

What the user can do with code
What obligations the user has

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Categories of Licences

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Not Licensed

Default state of code
Author has copyright
Cannot use

But can ask author for permission

Examples:

Blog posts
Websites

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Closed Source/Proprietary Licence

Generally can't use this code
Depends on the terms of the licence
Author retains copyright
Example:

EULA
Unity game engine

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Copyleft Open Source Licence

You can use this code!
But you have to share derivatives

Modifications or used as dependency

Author retains copyright
Examples:

GPL
AGPL
LGPL

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Permissive Open Source Licence

You can use this code!
Few restrictions
Author retains copyright
Examples:

MIT
BSD
Apache

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Public Domain

You can use this code!
No restrictions
Author has given up copyright
Examples:

Unlicense
CC0

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Joke Licences

Intent: permissive with humor
Actually: legally problematic
Don't use them!
Examples:

Beerware
WTFPL

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Common Licences

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MIT

Permissive licence
Must keep licence with code
Disclaims liability
Used by:

SQLAlchemy
Twisted
six

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BSD (2-clause & 3-clause)

Permissive licence
Must keep licence with source or binary
3-clause: usage doesn't allow endorsement
Used by:

numpy, scipy, pandas
Django, flask

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Apache 2.0

Permissive licence
Must keep licence with code
Grants patent rights
Used by:

requests
selenium
Android OS

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GPL

Strong copyleft licence
Must keep licence with code
Must share changes if distributed
Affects whole codebase
Used by:

Linux kernel (GPLv2)
Ansible (GLPv3)

GPL (GNU Public License)
Best known copyleft licence
Fairly long
Usual things - disclaimer of liability, copy of license with code
Like Apache: v3 includes grant of patent license
Copyleft stuff:
If you distribute the code, (or modify & distribute) must make source code available
If you don't redistribute code, (only personal use or company internal) you don't have to do anything special
Giving away or selling = make source code available
Additionally
If you include GPL dependency in your codebase (and distribute), you have to make the entire thing available under GPL
Copyleft = wants *keep* software free
Don't make something and not contribute back to community
Called 'viral' because including GPL'd code affects licensing of entire program
Definition of 'one problem' gets complicated
What's one program vs two that interact?

static & dynamic linking definitely yes, HTTP calls & piping output probably not, in between fuzzy

Where lawyers get involved (if using GPL dependency but not want to license GPL)
2 versions: v2 and v3 - interesting nuances but basically the same
Used by the Linux kernel & ansible

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Can I use that code?

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Closed source + MIT

Yes!
MIT only requires preserving licence

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Closed source + GPL

Probably not
Can be done through careful separation
Probably talk to a lawyer

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GPL + MIT

Yes!
MIT is less restrictive than GPL

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GPL + GPL

Yes!
Same licence, no problems

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MIT + MIT

Yes!
Same licence, no problems
MIT is very permissive

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MIT + GPL

Probably not
GPL requires derivatives licensed GPL

Could license under GPL instead of MIT

Could be done through careful separation
Probably talk to a lawyer

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Frequently Asked Questions

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Can I use code on Github?

It depends!
Not licensed by default
Check if the repository has a licence

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What about Stack Overflow?

Complicated :(
All user contributions are CC-BY-SA

But CC (probably) doesn't apply to code

Plans to move to MIT on hold
Uncertain if SO code is usable in projects

But good as inspiration

What about Stack Overflow?
Stack Overflow is complicated
User contributions are CC-BY-SA (copyleft for media), but it's not clear if CC applies to code

Usually text=CC, code=permissive
code isn't separately licensed

SO discussed moving to MIT (or modified MIT) in 2015/2016 but community politics happened, problems with proposition

Eg SO vs code review SE

Also complicated because not all snippets of code are big enough to be covered by copyright
Overall very awkward - I'm not going to make a recommendation
But will admit I use SO a lot when I'm programming for inspiration, reference, links etc
Extended discussion:

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Conclusion

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Take aways

Software licences are good
Software licences are hard
Permissive open source is easy to work with
GPL enforces software freedoms

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Check the licence!

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Thank you!

HollyBecker.net

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Resources & Bonus Slides

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Resources

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Contributor License Agreement (CLA)

Allow others to use & distribute your work
Often when contributing to a project
Allows project to defend license

Have legal docs saying they have copyright for all parts of the project

Github added implicit CLA (code licensed under repo license when make PR)

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LGPL

GPL family
Dynamic linking isn't a derivative work
Less viral
Easier to use in non-GPL projects

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AGPL

GPL family
Network access is distribution
Closes SAAS loophole

Don't want people using APGL code to run a website

Only GPLv3

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PyPI

Doesn't verify it has a licence to upload
Check!

Or ask maintainer to add a licence!