GPL PyQt with LGPL Qt

July 4, 2009

UPD: Actually, it turned out that if you don’t want to mess with manual installation of PyQt from sources, and also don’t wish to make fixes in its code, there are easy to use Windows installers on official PyQt page (GPL only). For Python 2.6 it can be downloaded here. Installation process is smooth and runs without any problems. And it DOES work from the scratch with LGPL version of Qt, remaining GPL itself though.

While configuring environment for developing my CD/DVD burner I ran into an issue with PyQt licensing. From my experience and what I heard previously and read in Internet, I was sure that “free” version of PyQt can be used with the “free” version of Qt library. But despite the fact I have LGPL Qt 4.5.2 installed on my Windows machine, the PyQt script kept telling me that those two libraries have inconsistent licenses. The error message lacks details:

Error: This version of PyQt and the Desktop edition of Qt have incompatible licenses.

That seemed kind of strange to me, so I started a little investigation. I found the initial (I suppose so) request for LGPL version of PyQt: [PyQt] LGPL license. There’s a rather long discussion, even with participation of PyQt author – Phil Thompson, which resulted in nothing. The main thought is that Phill was going to consider – should or not there be PyQt under LGPL.

Since that post was a somewhat outdated, headed back to PyQt site to check current situation and read the following:

PyQt, unlike Qt, is not available under the LGPL.

That stroke me, since I’m not sure if Qt is distributed under GPL at all nowadays. The thoughts started crowding in my head – how to overcome this obstacle (in a good sence). But then finally I’ve read the section named “Compatibility with Qt licenses”:

The GPL version of PyQt can be used with both the LGPL and GPL versions of Qt.

So there should be no problem develop in GPL PyQt with LGPL Qt library. But the script was resilient – “licenses are different!”. And I decided to dig into installation script with IDLE debugger. It turned out that during initial configuration, PyQt detects my LGPL QT as “Desktop” version and its own – as “GPL”, consequently the comparison of these two fails.

At that moment I decided try to just comment out the fancy function checkLicenses() – and it worked out! Now, after 1,5 hours of investigation, I have a working version of GPL PyQt with LGPL Qt!

P.S. Perhaps, there’s some additional info about how to make GPL PyQt work with LGPL Qt – I don’t know, as I wasn’t able to find any. So I made a fix that I think is a problem with PyQt installation script relying on information found at official site. It’s perhaps an inappropriate method, and I discourage you from using it πŸ˜‰

And, as it is stated in PyQt’s FAQ:

Riverbank is a product based software development company that depends on sales to fund PyQt’s continued development. […] An LGPL version of PyQt, while probably increasing the number of users, would result in a reduction in income and therefore our ability to fund future development.

So, no luck for us who wish to use PyQt under LGPL license.


In this post I’ll describe my experience during installation of PyQt on Windows platform. And I’ll post the mock-up which was promised in previous post in one of the following posts – I wasn’t yet able to find a decent and free tool for mock-ups creation.

So, to start you have to download and configure SIP -aΒ  tool for creation of C++ to Python bindings. This is essential to start work with PyQt.

  1. Unpack contents of SIP archive to some folder – preferably on the system disk (i.e. C:\)
  2. From the Start menu select the “Microsoft Visual Studio” -> “Visual Studio Tools” sub-item. Here run theΒ  “Visual Studio Command Prompt” with Administrator privileges (via right-click) – on Vista and Windows 7 SIP configuration script won’t be able to access system disk if it is not run with admin rights. If you use MinGW tools you can just start cmd.exe as Admin.
  3. In the opened command prompt go to SIP folder (in my case – C:\sip-4.8.1) and run the following command:
    python -p [your_platform]
    Replace the your_platform placeholder with real specification of the platform and compiler you use. For me it is: win32-msvc2005. The full list of supported platforms and compilers can be found at “\specs” folder.
  4. Now just run “nmake” and, after SIP is built, “nmake install” (“make” – for MinGW).

At this moment SIP is installed as a package into your Python.

Before building and installing PyQt you have to ensure that you have the following prerequisites:

  1. Installed Python and Qt. Please note that if you use commercial version of Qt, you’ll have to buy commercial PyQt also.
  2. Qt environment is set correctly: QTDIR environment variable points to to folder with Qt, and PATH includes the folder containing qmake.exe.

Now you are ready to build PyQt:

  1. Open cmd.exe in the same way as for the SIP.
  2. run
    nmake ("make" for MinGW)
    nmake install ("make install" for MinGW)

At this moment we are ready to start development with PyQt!

To start with, I’ll describe the development environment I’ll use to create my CD/DVD burner. Work progress will commence on Windows platform, since that OS is the most familiar for me.

The tools I’ll use:

  • ActiveState Active Python 2.6. That package is de-facto a standard for Windows.
  • ActiveState Komodo Edit. This editor is nice choice for developing in Python on Windows, though not ideal. I like, that Komode Edit is able to compose sources into workspaces, just like Visual Studio does πŸ™‚
  • Qt framework by Nokia for GUI. I’m in love with this library, and since it’s now redistributed under LGPL, my love have increased noticeably πŸ™‚ I will use Qt 4.5.2.
  • PyQt – Python bindings for Qt. I’m not yet familiar with PyQt and hope to get into it during the development process.

When Windows version will be ready I’llΒ  move on other platforms, and the toolset will surely be changed. But the set of software I specified should be sufficient for the initial release.

In the next post I’ll post the rough mock-up of my CD/DVD burner.


Here I’d like to share my goal for the next several weeks.

First of all, the main goal is to develop my skills in Python and to extend them as far as possible. To achieve this I decided, apart from reading books, to create a real application. So, the question was – what kind of software would be both interesting and challenging enough? Having though for a little time, I came with an idea: I’ll write a cross-platform CD/DVD burning application. And that’s why: I don’t like paying for software and I hate what Nero has turned into (a 700Mb monster), and none of free burning apps are good enough for me.

So, here are the main requirements for my future CD/DVD burner:

  1. Developed in Python. That’s point of the whole blog πŸ™‚
  2. The code has to be perfect, written in Python style (not C++) and be reusable (useful for others).
  3. Cross-platform. Yes, Python runs on many OS itself, but the domain-logic is hardly portable. Main targets are Windows, Linux and Mac OS.
  4. User-friendly UI – it should be better than average open-source one (you know, those ugly designs you cannot look at without tears in your eyes). In my opinion, it has to be fun to work with software. Since, I’m not a designer at all and the budget is $0, it’s gonna be somewhat difficult to achieve πŸ™‚
  5. It should be functional – be able to burn CDs/DVDs/Blu-Rays/Audio/Video/ISO and so on. In general, it should be able to work with any kind of media.
  6. The installation process has to be smooth and without a mess – in contradict to usual open-source software (./configure && make things)

So, the goal is set, the work is waiting. Hopefully this tale will be fun and educational. πŸ™‚