pyqt4 & qt license

[Michael Torrie]

On 03/09/2013 07:08 PM, pitsakis at gmail.com wrote:
> hello,
> 
> i want to develop a GUI application that will be sold. i want to use
> pyqt4. can i download and use the GPL version during the development
> and then buy the commercial verion beofore i distribute the
> application ?
> 
> commercial version means LGPL? i think i am comfused so please
> someone clarify on versions and licences.

Nope.  Commerical means you buy a royalty-free license to use their
product in a proprietary project.  In other words you buy the right to
use their code in a way that's compatible with your own code's
distribution scheme.

> 
> somewhere i also noticed that there is a qt license ? will i need
> this also ?

You must be aware of the licenses of each individual part of the stack
and honor their terms!  This is true of *any* library you use, and code
from *any* source.  Open source does not mean public domain and you
don't automatically have a right to use it in your own project.  If you
are using open source components in a proprietary project, you might
need to consult a lawyer if you are unsure of the use terms you are
dealing with or your obligations under those terms under copyright law.

You have to follow the appropriate license for Qt (LGPL, so no biggy for
you if you don't modify Qt itself), PyQt (GPL only or proprietary
royalty-free), Python itself (not a problem since you aren't modifying
it and you can redistribute it), and any and all Python libraries you
might use.  From what I can tell things in the standard library are
fine, but watch out for third-party libraries.  The licenses are not
always compatible with proprietary code.

As for PyQt, unless you pay for the proprietary, royalty-free license
for PyQT (before or after development), then you have to use the GPL for
your project, since those are the terms the free version of PyQt is
released under.  This is a deliberate choice by the company that makes
it to secure a revenue stream.

There is an alternative to PyQt, PySide, which is under the LGPL and
compatible with a closed-source project.