feat: remove Python 3.6 support (pybind#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 pybind#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>