ExtensionClass
Metaclass for subclassable extension types
Decision gist · record as of 2026-08-14
Yes, but only if you are maintaining a legacy Zope application or have a specific need to subclass C extension types. The package is actively maintained and has no known vulnerabilities. For new projects, use Python's built-in descriptor protocol and properties instead. Install friction is moderate due to compiled wheels, but prebuilt binaries are available for common platforms.AI-flagged interpretation of the facts on this page — verify before relying
Before you install
- Requires Python 3.10 or later; compiled C extension wheels are provided for common platforms but may require a C compiler on unsupported architectures.
- Medium install friction due to compiled wheels for multiple platforms and Python versions (3.10–3.14).
- Actively maintained with recent release (106 days ago) and ongoing support for new Python versions including free-threaded 3.14t.
License · maintenance · safety
ZPL-2.1 (unclear) — Licensed under ZPL-2.1 (Zope Public License 2.1), a permissive open-source license. License treatment is marked unclear in the fact sheet, so verify compatibility with your project's licensing requirements before use.
last release 2026-04-30 (106 days) · last repo commit 2026-08-14 · 4 stars
0 known vulnerabilities (OSV.dev, 2026-08-14) · 169,563 downloads/mo, #10,417 on PyPI
Alternatives
Verify before relying
import extensionclass
class MyExtension(extensionclass.ExtensionClass):
pass
obj = MyExtension()- Whether ZPL-2.1 is compatible with your project's license (marked unclear in metadata).
- Performance characteristics compared to modern Python descriptors and properties.
- Whether Acquisition wrapper semantics are still needed for your use case versus standard Python patterns.
What it is and what it does
ExtensionClass is a metaclass that allows classes defined in C extension modules to be subclassed from Python code—a capability not normally available with standard extension types. It also provides ComputedAttribute (similar to property but works on instances and preserves Acquisition semantics) and MethodObject (for attaching callable methods to extension classes). The package is primarily maintained for legacy Zope applications; modern Python code should use standard new-style classes and descriptors instead.
The package has no runtime dependencies and ships as compiled wheels for Python 3.10–3.14 across macOS (Intel and ARM64), Linux (i686, x86_64, aarch64), and Windows (x86_64 and ARM64). It is actively maintained and has been updated to support free-threaded Python 3.14t, though it is explicitly recommended only for applications that require it for backward compatibility.
Use it for
- Maintaining legacy Zope applications that depend on ExtensionClass-based object models.
- Subclassing C extension types when standard Python descriptors or properties are insufficient.
- Preserving Acquisition wrapper semantics in extension-based object hierarchies.
- Attaching computed attributes to extension class instances that behave like properties.
Worth the install?
AI-flagged interpretation of the facts on this page. Verify before relying on it.
Yes, but only if you are maintaining a legacy Zope application or have a specific need to subclass C extension types.
The package is actively maintained and has no known vulnerabilities. For new projects, use Python's built-in descriptor protocol and properties instead. Install friction is moderate due to compiled wheels, but prebuilt binaries are available for common platforms.
Install
extensionclass on PyPI
Before you install
Medium install friction due to compiled wheels for multiple platforms and Python versions (3.10–3.14). Actively maintained with recent release (106 days ago) and ongoing support for new Python versions including free-threaded 3.14t.
Requires Python 3.10 or later; compiled C extension wheels are provided for common platforms but may require a C compiler on unsupported architectures.
License in practice
Licensed under ZPL-2.1 (Zope Public License 2.1), a permissive open-source license. License treatment is marked unclear in the fact sheet, so verify compatibility with your project's licensing requirements before use.
Quickstart
import extensionclass
class MyExtension(extensionclass.ExtensionClass):
pass
obj = MyExtension()Verify before relying
- Whether ZPL-2.1 is compatible with your project's license (marked unclear in metadata).
- Performance characteristics compared to modern Python descriptors and properties.
- Whether Acquisition wrapper semantics are still needed for your use case versus standard Python patterns.
Package facts
| License | ZPL-2.1 unclear |
| Python support | Supports the current Python release >=3.10 |
| Install friction | Medium. Platform-specific wheel |
| Runtime dependencies | None |
| Maintenance | Actively maintained 106 days since the last release |
| Last repo commit | |
| First released | |
| Downloads | 169,563 / month, #10,417 on PyPI 30-day window, as of 2026-08-14 |
| Known vulnerabilities | None known OSV.dev, checked 2026-08-14 |
| Classifiers | Development Status :: 6 - MatureEnvironment :: Web EnvironmentFramework :: ZopeFramework :: Zope :: 5Operating System :: OS IndependentProgramming Language :: PythonProgramming Language :: Python :: 3Programming Language :: Python :: 3 :: OnlyProgramming Language :: Python :: 3.10Programming Language :: Python :: 3.11Programming Language :: Python :: 3.12Programming Language :: Python :: 3.13Programming Language :: Python :: 3.14Programming Language :: Python :: Implementation :: CPythonProgramming Language :: Python :: Implementation :: PyPy |
Evidence: extensionclass-6.3-cp310-cp310-macosx_10_9_x86_64.whl; extensionclass-6.3-cp310-cp310-macosx_11_0_arm64.whl; extensionclass-6.3-cp310-cp310-manylinux1_i686.manylinux2014_i686.manylinux_2_17_i686.manylinux_2_5_i686.whl; extensionclass-6.3-cp310-cp310-manylinux1_x86_64.manylinux2014_x86_64.manylinux_2_17_x86_64.manylinux_2_5_x86_64.whl; extensionclass-6.3-cp310-cp310-manylinux2014_aarch64.manylinux_2_17_aarch64.whl; extensionclass-6.3-cp310-cp310-win_amd64.whl; extensionclass-6.3-cp311-cp311-macosx_10_9_x86_64.whl; extensionclass-6.3-cp311-cp311-macosx_11_0_arm64.whl; extensionclass-6.3-cp311-cp311-manylinux1_i686.manylinux2014_i686.manylinux_2_17_i686.manylinux_2_5_i686.whl; extensionclass-6.3-cp311-cp311-manylinux1_x86_64.manylinux2014_x86_64.manylinux_2_17_x86_64.manylinux_2_5_x86_64.whl; extensionclass-6.3-cp311-cp311-manylinux2014_aarch64.manylinux_2_17_aarch64.whl; extensionclass-6.3-cp311-cp311-win_amd64.whl; extensionclass-6.3-cp311-cp311-win_arm64.whl; extensionclass-6.3-cp312-cp312-macosx_10_9_x86_64.whl; extensionclass-6.3-cp312-cp312-macosx_11_0_arm64.whl; extensionclass-6.3-cp312-cp312-manylinux1_i686.manylinux2014_i686.manylinux_2_17_i686.manylinux_2_5_i686.whl; extensionclass-6.3-cp312-cp312-manylinux1_x86_64.manylinux2014_x86_64.manylinux_2_17_x86_64.manylinux_2_5_x86_64.whl; extensionclass-6.3-cp312-cp312-manylinux2014_aarch64.manylinux_2_17_aarch64.whl; extensionclass-6.3-cp312-cp312-win_amd64.whl; extensionclass-6.3-cp312-cp312-win_arm64.whl
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