It’s been awhile since my last post, but there were so much happening in my personal life that I simple couldn’t find enough time to write a single post here. Nonetheless, I’ve finished reading the Bible of Python and have a lot of  thoughts from there. And I haven’t let go my idea to create a cross-platform CD/DVD burner in Python.

In this post I’d like to share my happiness around what I consider a significant event in the world of Python – the first public release of LGPL bindings for the perfect Nokia Qt frameworkPySide. At this moment the project is still in the process of development and stays in beta, but the plans are ambitious – to create an LGPL alternative for the PyQt.

So, what’s the PySide and why would world need another Python bindings for Qt. Let me cite the FAQ:

What about PyQt?

Nokia’s initial research into Python bindings for Qt involved speaking with Riverbank Computing, the makers of PyQt. We had several discussions with them to see if it was possible to use PyQt to achieve our goals. Unfortunately, a common agreement could not be found , so in the end we decided to proceed with PySide.

We will however maintain API compatibility with PyQt (you can use the same method names but can’t inter-operate with PyQt), at least for the initial release. To import PySide you have to use “import PySide” instead of “import PyQt4″.

One of the most important things about PySide is that it will maintain the API compatibility with PyQt! It means that you can just replace imports of PyQt with PySide and, viola!, everything works fine and you no more required to distribute under GPL terms.

I encourage everyone to give it a try, though at the moment only Unix version is available. If you interested in how it will go in future, you can read the PySide Roadmap.

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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 configure.py 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 configure.py 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 😉

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 -a  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 the  “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 configure.py -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
    python configure.py
    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 🙂
  • 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 🙂 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’ll  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.