[ci] Drop support for Python 3.7 and Python 3.8 (#6896)

* [ci] Drop support for Python 3.7 and Python 3.8

* Fix

* Bump numpy

* Fix

* fix comment, revert unrelated quoting changes

* add docs

---------
Co-authored-by: Nikita Titov <nekit94-08@mail.ru>
Co-authored-by: James Lamb <jaylamb20@gmail.com>

.appveyor.yml

@@ -3,7 +3,7 @@ version: 4.6.0.99.{build}
 image: Visual Studio 2015
 platform: x64
 configuration:
-  - '3.8'
+  - '3.9'
 
 # only build on 'master' and pull requests targeting it
 branches:

.ci/conda-envs/ci-core-py38.txt

-# [description]
-#
-#   Similar to ci-core.txt, but specific to Python 3.8.
-#
-#   Unlike ci-core.txt, this includes a Python version and uses
-#   `=` and `<=` pins to make solves faster and prevent against
-#   issues like https://github.com/microsoft/LightGBM/pull/6370.
-#
-# [usage]
-#
-#   conda create \
-#     --name test-env \
-#     --file ./.ci/conda-envs/ci-core-py38.txt
-#
-
-# python
-python=3.8.*
-
-# direct imports
-cffi=1.15.*
-dask=2023.5.*
-distributed=2023.5.*
-joblib=1.4.*
-matplotlib-base=3.7.*
-numpy=1.24.*
-pandas=1.5.*
-pyarrow-core=16.1.*
-python-graphviz=0.20.*
-scikit-learn=1.3.*
-scipy=1.10.*
-
-# testing-only dependencies
-cloudpickle=3.0.*
-pluggy=1.5.*
-psutil=5.9.8
-pytest=8.2.*
-
-# other recursive dependencies, just
-# pinned here to help speed up solves
-bokeh=3.1.*
-fsspec=2024.5.*
-# pinning 'libabseil' and 'libre2' to specific build numbers for pyarrow compatibility:
-# ref: https://github.com/microsoft/LightGBM/issues/6772
-libabseil=20240722.0=*_1
-libre2-11=2024.07.02=*_1
-msgpack-python=1.0.*
-pluggy=1.5.*
-pyparsing=3.1.4
-pytz=2024.1
-setuptools=69.5.*
-snappy=1.2.*
-tomli=2.0.*
-tornado=6.4.*
-wheel=0.43.*
-zict=3.0.*
-zipp=3.17.*

.ci/conda-envs/ci-core-py37.txt → .ci/conda-envs/ci-core-py39.txt

 # [description]
 #
-#   Similar to ci-core.txt, but specific to Python 3.7.
+#   Similar to ci-core.txt, but specific to Python 3.9.
 #
 #   Unlike ci-core.txt, this includes a Python version and uses
 #   `=` and `<=` pins to make solves faster and prevent against
@@ -10,27 +10,24 @@
 #
 #   conda create \
 #     --name test-env \
-#     --file ./.ci/conda-envs/ci-core-py37.txt
+#     --file ./.ci/conda-envs/ci-core-py39.txt
 #
 
 # python
-python=3.7.*
+python=3.9.*
 
 # direct imports
 cffi=1.15.*
-# older versions of Dask are incompatible with pandas>=2.0, but not all conda packages' metadata accurately reflects that
-#
-# ref: https://github.com/microsoft/LightGBM/issues/6030
-dask=2022.2.*
-distributed=2022.2.*
+# dask and distributed versions below are the first versions that support tornado >=6.2
+# which is required for testing
+dask=2022.12.*
+distributed=2022.12.*
 joblib=1.3.*
 matplotlib-base=3.5.*
-numpy=1.21.*
+numpy=1.22.*
 pandas=1.3.*
 pyarrow=9.0.*
-# python-graphviz 0.20.2 is not compatible with Python 3.7
-# ref: https://github.com/microsoft/LightGBM/pull/6370
-python-graphviz=0.20.1
+python-graphviz=0.20.*
 scikit-learn=1.0.*
 scipy=1.7.*
 
@@ -45,12 +42,11 @@ pytest=7.4.*
 bokeh=2.4.*
 fsspec=2023.1.*
 msgpack-python=1.0.*
-pluggy=1.0.*
 pytz=2024.1
 setuptools=59.8.*
 snappy=1.1.*
 tomli=2.0.*
-tornado=6.1.*
+tornado=6.2.*
 wheel=0.42.*
 zict=2.2.*
 zipp=3.15.*

.ci/pip-envs/requirements-oldest.txt

@@ -6,7 +6,7 @@
 # see https://devguide.python.org/versions/
 #
 cffi==1.15.1
-numpy==1.19.0
+numpy==1.19.3
 pandas==1.1.3
 pyarrow==6.0.1
 scikit-learn==0.24.2

.ci/test-windows.ps1

@@ -68,10 +68,8 @@ conda activate
 conda config --set always_yes yes --set changeps1 no
 conda update -q -y conda "python=$env:PYTHON_VERSION[build=*_cp*]"
 
-if ($env:PYTHON_VERSION -eq "3.7") {
-    $env:CONDA_REQUIREMENT_FILE = "$env:BUILD_SOURCESDIRECTORY/.ci/conda-envs/ci-core-py37.txt"
-} elseif ($env:PYTHON_VERSION -eq "3.8") {
-    $env:CONDA_REQUIREMENT_FILE = "$env:BUILD_SOURCESDIRECTORY/.ci/conda-envs/ci-core-py38.txt"
+if ($env:PYTHON_VERSION -eq "3.9") {
+    $env:CONDA_REQUIREMENT_FILE = "$env:BUILD_SOURCESDIRECTORY/.ci/conda-envs/ci-core-py39.txt"
 } else {
     $env:CONDA_REQUIREMENT_FILE = "$env:BUILD_SOURCESDIRECTORY/.ci/conda-envs/ci-core.txt"
 }

.ci/test.sh

@@ -160,10 +160,8 @@ if [[ $TASK == "check-docs" ]] || [[ $TASK == "check-links" ]]; then
     exit 0
 fi
 
-if [[ $PYTHON_VERSION == "3.7" ]]; then
-    CONDA_REQUIREMENT_FILE="${BUILD_DIRECTORY}/.ci/conda-envs/ci-core-py37.txt"
-elif [[ $PYTHON_VERSION == "3.8" ]]; then
-    CONDA_REQUIREMENT_FILE="${BUILD_DIRECTORY}/.ci/conda-envs/ci-core-py38.txt"
+if [[ $PYTHON_VERSION == "3.9" ]]; then
+    CONDA_REQUIREMENT_FILE="${BUILD_DIRECTORY}/.ci/conda-envs/ci-core-py39.txt"
 else
     CONDA_REQUIREMENT_FILE="${BUILD_DIRECTORY}/.ci/conda-envs/ci-core.txt"
 fi

.github/workflows/python_package.yml

@@ -165,10 +165,10 @@ jobs:
     strategy:
       fail-fast: false
       matrix:
-        # end-of-life Python versions
+        # This should always include at least the oldest
+        # not-yet-end-of-life Python version
         python_version:
-          - '3.7'
-          - '3.8'
+          - '3.9'
     steps:
       - name: Checkout repository
         uses: actions/checkout@v4

python-package/README.rst

@@ -333,6 +333,12 @@ Examples
 
 Refer to the walk through examples in `Python guide folder <https://github.com/microsoft/LightGBM/tree/master/examples/python-guide>`_.
 
+Supported Python Versions
+-------------------------
+
+This project supports all Python versions until they reach end-of-life.
+For details on the support calendar for Python versions, see https://devguide.python.org/versions/.
+
 Development Guide
 -----------------
 

python-package/pyproject.toml

@@ -10,8 +10,6 @@ classifiers = [
     "Operating System :: POSIX",
     "Operating System :: Unix",
     "Programming Language :: Python :: 3",
-    "Programming Language :: Python :: 3.7",
-    "Programming Language :: Python :: 3.8",
     "Programming Language :: Python :: 3.9",
     "Programming Language :: Python :: 3.10",
     "Programming Language :: Python :: 3.11",
@@ -30,7 +28,7 @@ maintainers = [
 ]
 name = "lightgbm"
 readme = "README.rst"
-requires-python = ">=3.7"
+requires-python = ">=3.9"
 version = "4.6.0.99"
 
 [project.optional-dependencies]
@@ -103,7 +101,7 @@ exclude = [
 line-length = 120
 
 # this should be set to the oldest version of python LightGBM supports
-target-version = "py37"
+target-version = "py39"
 
 [tool.ruff.format]
 docstring-code-format = false