Remove Python 3.8 support

This commit removes support for Python 3.8, mostly by deleting
workarounds and corner cases related to this old Python version.

Author: wjakob

.github/workflows/ci.yml

@@ -21,7 +21,7 @@ jobs:
       fail-fast: false
       matrix:
         os: ['ubuntu-latest', 'windows-2022', 'macos-13']
-        python: ['3.8', '3.9', '3.10', '3.11', '3.12', '3.13', '3.14', 'pypy3.9-v7.3.16', 'pypy3.10-v7.3.17']
+        python: ['3.9', '3.10', '3.11', '3.12', '3.13', '3.14', 'pypy3.9-v7.3.16', 'pypy3.10-v7.3.17']
 
     name: "Python ${{ matrix.python }} / ${{ matrix.os }}"
     runs-on: ${{ matrix.os }}

CMakeLists.txt

@@ -145,7 +145,7 @@ if (NOT TARGET Python::Module OR NOT TARGET Python::Interpreter)
     set(NB_PYTHON_DEV_MODULE Development.Module)
   endif()
 
-  find_package(Python 3.8
+  find_package(Python 3.9
     REQUIRED COMPONENTS Interpreter ${NB_PYTHON_DEV_MODULE}
     OPTIONAL_COMPONENTS Development.SABIModule)
 endif()

cmake/collect-symbols.py

@@ -10,7 +10,7 @@
 
 funcs: "set[str]" = set()
 
-for ver in ['3.7', '3.8', '3.9']:
+for ver in ['3.9']:
   url = f'https://raw.githubusercontent.com/python/cpython/{ver}/PC/python3.def'
   output = urlopen(url).read().decode('utf-8')
   for match in re.findall(r"  (.*)=.*", output):

cmake/nanobind-config.cmake

@@ -4,6 +4,10 @@ if (NOT TARGET Python::Module)
   message(FATAL_ERROR "You must invoke 'find_package(Python COMPONENTS Interpreter Development REQUIRED)' prior to including nanobind.")
 endif()
 
+if (Python_VERSION VERSION_LESS "3.9")
+  message(FATAL_ERROR "nanobind requires Python 3.9 or newer (found Python ${Python_VERSION}).")
+endif()
+
 # Determine the right suffix for ordinary and stable ABI extensions.
 
 # We always need to know the extension

docs/api_core.rst

@@ -2158,9 +2158,6 @@ declarations in generated :ref:`stubs <stubs>`,
    See the section on :ref:`creating generic types <typing_generics_creating>`
    for an example.
 
-   This feature is only supported on Python 3.9+. Nanobind will ignore
-   the attribute in Python 3.8 builds.
-
 .. cpp:struct:: template <typename T> supplement
 
    Indicate that ``sizeof(T)`` bytes of memory should be set aside to

docs/building.rst

@@ -20,7 +20,7 @@ Preliminaries
 Begin by creating a new file named ``CMakeLists.txt`` in the root directory of
 your project. It should start with the following lines that declare a project
 name and tested CMake version range. The third line line searches for Python >=
-3.8 including the ``Development.Module`` component required by nanobind. The
+3.9 including the ``Development.Module`` component required by nanobind. The
 name of this module changed across CMake versions, hence the additional
 conditional check.
 
@@ -35,7 +35,7 @@ conditional check.
       set(DEV_MODULE Development.Module)
     endif()
 
-    find_package(Python 3.8 COMPONENTS Interpreter ${DEV_MODULE} REQUIRED)
+    find_package(Python 3.9 COMPONENTS Interpreter ${DEV_MODULE} REQUIRED)
 
 Add the following lines below. They configure CMake to perform an optimized
 *release* build by default unless another build type is specified. Without this

docs/exceptions.rst

@@ -266,8 +266,8 @@ Should they throw or fail to catch any exceptions in their call graph,
 the C++ runtime calls ``std::terminate()`` to abort immediately.
 
 Similarly, Python exceptions raised in a class's ``__del__`` method do not
-propagate, but are logged by Python as an unraisable error. In Python 3.8+, a
-`system hook is triggered
+propagate, but are logged by Python as an unraisable error. A `system hook is
+triggered
 <https://docs.python.org/3/library/sys.html#sys.unraisablehook>`_
 and an auditing event is logged.
 

docs/index.rst

@@ -54,7 +54,7 @@ similar runtime performance).
 
 nanobinds depends on
 
-- **Python 3.8+** or **PyPy 7.3.10+** (the *3.8* and *3.9* PyPy flavors are
+- **Python 3.9+** or **PyPy 7.3.10+** (the *3.9* and *3.10* PyPy flavors are
   supported, though there are :ref:`some limitations <pypy_issues>`).
 - **CMake 3.15+**.
 - **A C++17 compiler**: Clang 8+, GCC 8+, MSVC2019+, MinGW-w64, Intel ICX

docs/packaging.rst

@@ -101,7 +101,7 @@ An example is shown below:
    version = "0.0.1"
    description = "A brief description of what this project does"
    readme = "README.md"
-   requires-python = ">=3.8"
+   requires-python = ">=3.9"
    authors = [
        { name = "Your Name", email = "[email protected]" },
    ]
@@ -178,7 +178,7 @@ component that can be used to create `stable ABI
 .. code-block:: cmake
 
    # Try to import all Python components potentially needed by nanobind
-   find_package(Python 3.8
+   find_package(Python 3.9
      REQUIRED COMPONENTS Interpreter Development.Module
      OPTIONAL_COMPONENTS Development.SABIModule)
 
@@ -316,7 +316,6 @@ block to remove incompatible configurations from the matrix:
 
 .. code-block:: toml
 
-    skip = ["cp38-*", "pp38-*"] # Skip CPython and PyPy 3.8
     archs = ["auto64"]          # Only target 64 bit architectures
 
 The `cibuildwheel documentation

docs/refleaks.rst

@@ -337,11 +337,9 @@ Here is an example of the required code for a ``Wrapper`` type:
    struct Wrapper { std::shared_ptr<Wrapper> value; };
 
    int wrapper_tp_traverse(PyObject *self, visitproc visit, void *arg) {
-       // On Python 3.9+, we must traverse the implicit dependency
-       // of an object on its associated type object.
-       #if PY_VERSION_HEX >= 0x03090000
-           Py_VISIT(Py_TYPE(self));
-       #endif
+       // We must traverse the implicit dependency of an object on its
+       // associated type object.
+       Py_VISIT(Py_TYPE(self));
 
        // The tp_traverse method may be called after __new__ but before or during
        // __init__, before the C++ constructor has been completed. We must not
@@ -454,28 +452,6 @@ how deal with them. For completeness, let's consider some other possibilities.
   should be fixed in the responsible framework so that leak warnings aren't
   cluttered with flukes and can be more broadly useful.
 
-- **Older Python versions**: Very old Python versions (e.g., 3.8) don't
-  do a good job cleaning up global references when the interpreter shuts down.
-  The following code may leak a reference if it is a top-level statement in a
-  Python file or the REPL.
-
-  .. code-block:: python
-
-     a = my_ext.MyObject()
-
-  Such a warning is benign and does not indicate an actual leak. It simply
-  highlights a flaws in the interpreter shutdown logic of old Python versions.
-  Wrap your code into a function to address this issue even on such versions:
-
-  .. code-block:: python
-
-     def run():
-         a = my_ext.MyObject()
-         # ...
-
-     if __name__ == '__main__':
-         run()
-
 - **Exceptions**. Some exceptions such as ``AttributeError`` have been observed
   to hold references, e.g. to the object which lacked the desired attribute. If
   the last exception raised by the program references a nanobind instance, then