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Re: OT ? PyQt: how is the commercial license not GPL ?



On Mon, 2009-01-19 at 13:48 -0700, Linuxguy123 wrote:
> I'm looking at using PyQt for a project. 
> 
> I've gone to the Riverbank Computing homepage to learn more about PyQT
> and I ran into the following.
> (http://www.riverbankcomputing.co.uk/commercial/pyqt)
> 
> ==========================================================================
> PyQt Commercial Version
> Like Qt itself, PyQt is provided under a number of licenses depending on
> how it is going to be used. In fact, we try and follow Trolltech's
> licensing model as closely as we can.
> ==========================================================================
> 
> Comment: As far as I know, this page is out of date.  Nokia bought
> Trolltech and Qt is licensed under either GPL or LGPL.
> 
> Anyway... carrying on... 
> 
> ============================================================================
> The free version of PyQt is licensed under the GNU General Public
> License. If your use of PyQt is compatible with the GPL then you do not
> need to buy a commercial PyQt license. Similarly you do not need to buy
> a commercial Qt license. 
> <snip> 
> If your use of PyQt is not compatible with the GPL then you require a
> commercial PyQt license.
> ===========================================================================
> 
> So if I buy a "commercial license" from Riverbank, I can violate the
> GPL ?  I don't get this.

Yes.  They own the code.  If you get the GPL version, you can do what
the GPL permits.  If you want to do something the GPL does not permit,
you need a different license to do so.

> 
> The website goes on...
> 
> ===========================================================================
> There is no functional difference between the GPL version and the
> commercial version of PyQt.
> ===========================================================================
> 
> But I am supposed to buy a license to use it ?

Only if you want to use it in a way the GPL does not permit.

> 
> 
> ===========================================================================
> What Does the Commercial Version Give Me?
> A copy of the commercial license gives you the following.
> 
>       * A copy of the PyQt source code that you download via HTTP.
> ===========================================================================
> 
> Doesn't the GPL require this for all applications ?

The GPL requires that the source must be made available to anyone you
distribute the program to.  For programs that compile to binaries,
making source available is an additional requirement.  For scripting
languages, it's hard to keep the source hidden and still distribute the
program.

> 
> 
> 
> ==========================================================================
>       * A copy of the QScintilla source code that you download via HTTP.
>       * The right for a single developer to write applications under
>         Windows, UNIX, Linux and MacOS/X.
> ==========================================================================
> 
> Doesn't the GPL say that anyone can use it for any reason ?

Yes, for your own use.  What the GPL restricts is *redistribution*.  You
can only redistribute if you adhere to the terms of the GPL.

So this is the crux of the matter.  If you want to redistribute the code
or a derivative work under terms that violate the GPL, you need a
license to do so.

> 
> 
> ==========================================================================
>       * The right to distribute the required PyQt modules and QScintilla
>         library with your applications so long as the users of those
>         applications do not themselves have direct access to PyQt.
>         Otherwise those users themselves become developers and require
>         their own copies of the commercial versions of both PyQt and Qt.
> =========================================================================
> 
> I really don't understand that.  I thought that developers had to
> distribute code when they shipped a GPL product.

But if you distribute the same code under another license, the
recipients must respect that license.  They can get a copy under the
GPL, but then they have to respect the terms of the GPL when they
redistribute it.

> 
> I ask these questions because 
> 
> a) Fedora is providing the PyQt library and source in the repositories
> and surely someone somewhere in the Fedora community has encountered
> this before me.

They distribute the GPL version.  You can redistribute that code only if
you respect the terms of the GPL.

> 
> b) I don't see a "Licensing" page on the Riverbank web page that might
> explain what they are trying to accomplish with the commercial license.

They are trying to make money 8^).  One way they can do so is by
charging you for the right to redistribute their code under terms
outside the scope of the GPL.

> 
> Thanks for listening.

HTH.

> 
> LinuxGuy
> 
> 
> 
> 
> 
-- 
                Matthew Saltzman

Clemson University Math Sciences
mjs AT clemson DOT edu
http://www.math.clemson.edu/~mjs


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