Yes, Python Qt bindings can be used for free, but the terms of "free" depend significantly on which binding you choose and how you intend to use it. The primary "Python Qt" implementations are PyQt and PySide, each offering distinct licensing models that are crucial for developers to understand, especially for commercial applications.
Understanding "Python Qt" and Its Implementations
When developers refer to "Python Qt," they are typically talking about Python bindings that allow them to use the powerful Qt framework for creating graphical user interfaces (GUIs) with Python. Qt is a cross-platform C++ framework, and these bindings make its extensive capabilities accessible to Python developers. The two leading options are:
- PyQt: Developed by the British firm Riverbank Computing, it was one of the first and most widely adopted Qt bindings for Python.
- PySide (also known as Qt for Python): This is the official Python binding maintained by The Qt Company itself, offering direct integration and support for the latest Qt versions.
PyQt: Licensing Details
PyQt, developed by Riverbank Computing, is considered free software. Historically, and mirroring the terms of Qt versions older than 4.5, PyQt has been available under a variety of licenses, notably including the GNU General Public License (GPL) and a commercial license. It's important to highlight that under these specific historical terms, the GNU Lesser General Public License (LGPL) was not among the primary distribution licenses offered for PyQt itself.
Currently, PyQt (e.g., PyQt6) is primarily available under two main licenses:
- GNU General Public License (GPLv3): This means if you use PyQt in your application, your entire application must also be licensed under a compatible GPL license. This often implies that your application's source code must be made publicly available if you distribute the application.
- Commercial License: For developers who wish to create proprietary, closed-source applications without adhering to the GPL's open-source requirements, a commercial license can be purchased from Riverbank Computing. This provides the flexibility to distribute your software without revealing its source code.
Key takeaway for PyQt: If you're developing a closed-source commercial application and don't want to purchase a commercial license, PyQt's GPL terms make it unsuitable.
PySide: The Official LGPL Option
PySide, the official Qt for Python project, offers a more permissive licensing model that is often preferred by developers building proprietary applications.
- GNU Lesser General Public License (LGPLv3): PySide is available under the LGPLv3. This license is generally more flexible than the standard GPL. It allows you to use PySide in both free and proprietary (closed-source) applications without necessarily having to release the source code of your entire application. You typically only need to make sure that the PySide components themselves remain modifiable and that you provide a way for users to obtain and modify the PySide source code if they wish.
- Commercial License: Like the underlying Qt framework, PySide can also be used under commercial terms for those requiring specific enterprise support or additional guarantees.
Key takeaway for PySide: Its LGPL license makes it a popular choice for commercial developers who need to create closed-source applications without incurring licensing fees, provided they comply with the LGPL's terms (e.g., dynamic linking, providing attribution).
Key Differences: PyQt vs. PySide
While both PyQt and PySide enable Python developers to create Qt-based GUIs, their licensing and other aspects lead to significant differences.
| Feature | PyQt | PySide (Qt for Python) |
|---|---|---|
| Maintainer | Riverbank Computing | The Qt Company (official) |
| Primary License | GPLv3 (or Commercial) | LGPLv3 (or Commercial) |
| Commercial Use | Requires GPL compliance or commercial license purchase | Permitted under LGPLv3 with less restrictive terms |
| API Syntax | Very similar to Qt C++, some minor differences | Fully aligned with Qt C++ API, officially supported |
| Community | Large, well-established | Growing, official support from Qt Company |
| Availability | Widely used for a long time, stable releases | Newer, actively developed, keeps pace with Qt releases |
Other considerations:
- Community and Support: PyQt has a long history and a very mature community. PySide, being official, benefits from direct support and development by The Qt Company.
- Compatibility: Both aim for high compatibility with the underlying Qt framework, but PySide often aligns more closely with the very latest Qt features due to its official status.
Choosing the Right Python Qt Binding for Your Project
Selecting between PyQt and PySide depends heavily on your project's licensing requirements and your development philosophy.
- For Open-Source Projects: Both PyQt (GPL) and PySide (LGPL) are excellent choices. If you're happy to release your entire application under GPL, PyQt is perfectly fine. If you prefer a more permissive license for your open-source project, PySide (LGPL) might be a better fit.
- For Proprietary/Commercial Closed-Source Applications (No Budget for Commercial License):
- PySide (LGPL) is generally the recommended choice. Its LGPL license allows you to use the library in closed-source applications without having to purchase a commercial license, provided you comply with the LGPL's terms (e.g., dynamic linking and allowing users to replace the PySide library).
- PyQt (GPL) is not suitable for closed-source commercial applications unless you purchase a commercial license from Riverbank Computing.
- For Proprietary/Commercial Closed-Source Applications (With Budget for Commercial License): Both PyQt and PySide offer commercial licenses that provide maximum flexibility, dedicated support, and assurance for proprietary development.
FAQs about Python Qt Licensing
Q: Can I use PyQt for free in a closed-source commercial application?
A: No, not without purchasing a commercial license from Riverbank Computing. The free version of PyQt is licensed under GPL, which requires your application to also be open source.
Q: Can I use PySide for free in a closed-source commercial application?
A: Yes, generally. PySide is licensed under LGPL, which permits its use in proprietary applications without requiring you to make your entire application's source code public. You must, however, comply with the LGPL's specific terms, such as dynamically linking to the library and allowing users to replace the LGPL components.
Q: What if I only use Python Qt for internal tools, not for external distribution?
A: If your application is for internal use only and never distributed outside your organization, the licensing restrictions typically do not apply as strictly. However, it's always best to consult the specific license terms or legal counsel for absolute clarity, especially in larger corporate environments.
Q: Is the underlying Qt framework free?
A: Yes, the Qt framework itself is available under various open-source licenses, including GPL and LGPL, and also under a commercial license. The specific license you choose for Qt itself (when developing in C++) would have similar implications for your project. Python bindings like PySide often directly leverage the LGPL option of Qt.
