feat: remove Python 3.6 support (#5177)

* Change Python version guard: PYTHON < 3.7 IS UNSUPPORTED.

* Replace or remove Python 3.6 jobs.

* Move appveyor to Python 3.8

* Change `[tool.pylint]` `master.py-version` from `3.6` to `3.8`

* Change `[tool.pylint]` `master.py-version` to `3.7`

* Remove `centos:7` job; Change almalinux:8 job to use Python 3.8

* Try 🐍 3.8 • ubuntu-20.04 • x64 without `-DCMAKE_CXX_FLAGS="-D_=1"`

* Update setup.cfg as suggested by @henryiii

* Try running `cmake --build . --target cpptest` on all platforms (`standard` job).

* Disable deadsnakes jobs entirely.

* Apply PR #5179: Add Python 3.10, 3.11, 3.12 to win32 job matrix.

* Add back `-DCMAKE_CXX_FLAGS="-D_=1"` but do not install boost in that case.

* PY_VERSION_HEX < 3.7 cleanup pass: include/pybind11

* WITH_THREAD cleanup pass: include/pybind11

* Undo incorrect change.

* Revert "Disable deadsnakes jobs entirely."

This reverts commit bbcd008.

* WITH_THREAD cleanup pass: tests/

* Change Python version guard in pybind11/__init__.py: pybind11 does not support Python < 3.7.

* Misc cleanup pass

* chore: use future imports

Signed-off-by: Henry Schreiner <henryschreineriii@gmail.com>

* Update tests/test_numpy_array.py

* Update test_numpy_array.py

---------

Signed-off-by: Henry Schreiner <henryschreineriii@gmail.com>
Co-authored-by: Henry Schreiner <henryschreineriii@gmail.com>

.appveyor.yml

@@ -9,7 +9,7 @@ platform:
 - x86
 environment:
  matrix:
- - PYTHON: 36
+ - PYTHON: 38
  CONFIG: Debug
 install:
 - ps: |

.github/workflows/ci.yml

@@ -32,7 +32,7 @@ jobs:
  matrix:
  runs-on: [ubuntu-20.04, windows-2022, macos-13]
  python:
- - '3.6'
+ - '3.8'
  - '3.9'
  - '3.12'
  - '3.13'
@@ -48,16 +48,17 @@ jobs:
  include:
  # Just add a key
  - runs-on: ubuntu-20.04
- python: '3.6'
+ python: '3.8'
  args: >
  -DPYBIND11_FINDPYTHON=ON
  -DCMAKE_CXX_FLAGS="-D_=1"
+ exercise_D_: 1
  - runs-on: ubuntu-20.04
  python: 'pypy-3.8'
  args: >
  -DPYBIND11_FINDPYTHON=ON
  - runs-on: windows-2019
- python: '3.6'
+ python: '3.8'
  args: >
  -DPYBIND11_FINDPYTHON=ON
  # Inject a couple Windows 2019 runs
@@ -82,7 +83,7 @@ jobs:
 
  - name: Setup Boost (Linux)
  # Can't use boost + define _
- if: runner.os == 'Linux' && matrix.python != '3.6'
+ if: runner.os == 'Linux' && matrix.exercise_D_ != 1
  run: sudo apt-get install libboost-dev
 
  - name: Setup Boost (macOS)
@@ -655,15 +656,13 @@ jobs:
  cmake --build build-17 --target test_cmake_build
 
 
- # Testing on CentOS (manylinux uses a centos base, and this is an easy way
- # to get GCC 4.8, which is the manylinux1 compiler).
+ # Testing on CentOS (manylinux uses a centos base).
  centos:
  runs-on: ubuntu-latest
  strategy:
  fail-fast: false
  matrix:
  container:
- - "centos:7" # GCC 4.8
  - "almalinux:8"
  - "almalinux:9"
 
@@ -673,18 +672,13 @@ jobs:
  steps:
  - name: Latest actions/checkout
  uses: actions/checkout@v4
- if: matrix.container != 'centos:7'
-
- - name: Pin actions/checkout as required for centos:7
- uses: actions/checkout@v3
- if: matrix.container == 'centos:7'
 
- - name: Add Python 3 (RHEL 7)
- if: matrix.container == 'centos:7'
- run: yum update -y && yum install -y python3-devel gcc-c++ make git
+ - name: Add Python 3.8
+ if: matrix.container == 'almalinux:8'
+ run: dnf update -y && dnf install -y python38-devel gcc-c++ make git
 
- - name: Add Python 3 (RHEL 8+)
- if: matrix.container != 'centos:7'
+ - name: Add Python 3 (default)
+ if: matrix.container != 'almalinux:8'
  run: dnf update -y && dnf install -y python3-devel gcc-c++ make git
 
  - name: Update pip
@@ -807,7 +801,6 @@ jobs:
  fail-fast: false
  matrix:
  python:
- - '3.6'
  - '3.7'
  - '3.8'
  - '3.9'

.github/workflows/pip.yml

@@ -21,19 +21,18 @@ env:
 
 jobs:
  # This builds the sdists and wheels and makes sure the files are exactly as
- # expected. Using Windows and Python 3.6, since that is often the most
- # challenging matrix element.
+ # expected.
  test-packaging:
- name: 🐍 3.6 • 📦 tests • windows-latest
+ name: 🐍 3.8 • 📦 tests • windows-latest
  runs-on: windows-latest
 
  steps:
  - uses: actions/checkout@v4
 
- - name: Setup 🐍 3.6
+ - name: Setup 🐍 3.8
  uses: actions/setup-python@v5
  with:
- python-version: 3.6
+ python-version: 3.8
 
  - name: Prepare env
  run: |

README.rst

@@ -34,7 +34,7 @@ dependency.
 Think of this library as a tiny self-contained version of Boost.Python
 with everything stripped away that isn't relevant for binding
 generation. Without comments, the core header files only require ~4K
-lines of code and depend on Python (3.6+, or PyPy) and the C++
+lines of code and depend on Python (3.7+, or PyPy) and the C++
 standard library. This compact implementation was possible thanks to
 some C++11 language features (specifically: tuples, lambda functions and
 variadic templates). Since its creation, this library has grown beyond
@@ -79,7 +79,7 @@ Goodies
 In addition to the core functionality, pybind11 provides some extra
 goodies:
 
-- Python 3.6+, and PyPy3 7.3 are supported with an implementation-agnostic
+- Python 3.7+, and PyPy3 7.3 are supported with an implementation-agnostic
  interface (pybind11 2.9 was the last version to support Python 2 and 3.5).
 
 - It is possible to bind C++11 lambda functions with captured

docs/benchmark.py

@@ -1,3 +1,5 @@
+from __future__ import annotations
+
 import datetime as dt
 import os
 import random

docs/compiling.rst

@@ -426,7 +426,7 @@ with ``PYTHON_EXECUTABLE``. For example:
 
 .. code-block:: bash
 
- cmake -DPYBIND11_PYTHON_VERSION=3.6 ..
+ cmake -DPYBIND11_PYTHON_VERSION=3.7 ..
 
  # Another method:
  cmake -DPYTHON_EXECUTABLE=/path/to/python ..
@@ -493,7 +493,7 @@ existing targets instead:
  cmake_minimum_required(VERSION 3.15...3.22)
  project(example LANGUAGES CXX)
 
- find_package(Python 3.6 COMPONENTS Interpreter Development REQUIRED)
+ find_package(Python 3.7 COMPONENTS Interpreter Development REQUIRED)
  find_package(pybind11 CONFIG REQUIRED)
  # or add_subdirectory(pybind11)
 

docs/conf.py

@@ -11,6 +11,7 @@
 #
 # All configuration values have a default; values that are commented out
 # serve to show the default.
+from __future__ import annotations
 
 import os
 import re

include/pybind11/detail/class.h

@@ -567,17 +567,9 @@ inline void enable_dynamic_attributes(PyHeapTypeObject *heap_type) {
  type->tp_traverse = pybind11_traverse;
  type->tp_clear = pybind11_clear;
 
- static PyGetSetDef getset[] = {{
-#if PY_VERSION_HEX < 0x03070000
- const_cast<char *>("__dict__"),
-#else
- "__dict__",
-#endif
- PyObject_GenericGetDict,
- PyObject_GenericSetDict,
- nullptr,
- nullptr},
- {nullptr, nullptr, nullptr, nullptr, nullptr}};
+ static PyGetSetDef getset[]
+ = {{"__dict__", PyObject_GenericGetDict, PyObject_GenericSetDict, nullptr, nullptr},
+ {nullptr, nullptr, nullptr, nullptr, nullptr}};
  type->tp_getset = getset;
 }
 

include/pybind11/detail/common.h

@@ -272,9 +272,8 @@ PYBIND11_WARNING_DISABLE_MSVC(4505)
 #endif
 
 #include <Python.h>
-// Reminder: WITH_THREAD is always defined if PY_VERSION_HEX >= 0x03070000
-#if PY_VERSION_HEX < 0x03060000
-# error "PYTHON < 3.6 IS UNSUPPORTED. pybind11 v2.9 was the last to support Python 2 and 3.5."
+#if PY_VERSION_HEX < 0x03070000
+# error "PYTHON < 3.7 IS UNSUPPORTED. pybind11 v2.12 was the last to support Python 3.6."
 #endif
 #include <frameobject.h>
 #include <pythread.h>