Warn on Python 3.10 that 0.15 will not support it

- DeprecationWarning at import time below the interpreter floor of 0.15
- the floor as one constant, the check as a function taking the version
- pyproject comment on the requires-python line to raise in 0.15
- test both branches of the check on any interpreter

Author: OCCAM Coder

numpy_groupies/__init__.py

@@ -1,5 +1,7 @@
 from __future__ import annotations
 
+import sys
+import warnings
 from typing import TYPE_CHECKING, Any
 
 from numpy_groupies.aggregate_purepy import aggregate as aggregate_py
@@ -90,3 +92,29 @@ def uaggregate(
     else:
         __version__ = get_version(root="..", relative_to=__file__)
         del get_version
+
+
+# the interpreter floor of the next minor release - 0.14 is the last version
+# that runs below it, 0.15 is the first one that will not
+_next_release_floor = (3, 11)
+
+
+def _warn_python_eol(version_info, floor=_next_release_floor):
+    """The end-of-support notice for an interpreter older than *floor*.
+
+    Takes the version as an argument rather than reading ``sys.version_info``
+    itself so that both of its branches are testable on any interpreter, and so
+    that dropping 3.10 for real is a change of the one constant above.
+    """
+    if tuple(version_info[:2]) < tuple(floor):
+        running = ".".join(str(part) for part in tuple(version_info[:3]))
+        required = ".".join(str(part) for part in floor)
+        warnings.warn(
+            f"numpy-groupies will require Python {required} or newer from version 0.15, "
+            f"and the 0.14 releases are the last to support this interpreter ({running}).",
+            DeprecationWarning,
+            stacklevel=2,
+        )
+
+
+_warn_python_eol(sys.version_info)

numpy_groupies/tests/test_python_eol.py

@@ -0,0 +1,30 @@
+"""The end-of-support notice of ``numpy_groupies`` for old interpreters.
+
+The package warns while it is imported, but the check takes the interpreter
+version as an argument, so both of its branches run on whatever interpreter the
+suite happens to use.
+"""
+
+from warnings import catch_warnings, simplefilter
+
+import pytest
+
+from numpy_groupies import _warn_python_eol
+
+
+@pytest.mark.parametrize("version_info", [(3, 11), (3, 12), (3, 14), (3, 15)])
+def test_supported_interpreters_stay_quiet(version_info):
+    # the filter turns every warning into an error, so getting out of the block
+    # at all is the assertion
+    with catch_warnings():
+        simplefilter("error")
+        _warn_python_eol(version_info)
+
+
+@pytest.mark.parametrize("version_info", [(3, 9), (3, 10), (3, 10, 12)])
+def test_the_dropped_interpreter_is_warned(version_info):
+    with pytest.warns(DeprecationWarning) as record:
+        _warn_python_eol(version_info)
+    message = str(record[-1].message)
+    assert "Python 3.11 or newer from version 0.15" in message
+    assert ".".join(str(part) for part in version_info) in message

pyproject.toml

@@ -32,7 +32,7 @@ classifiers = [
     "Topic :: Software Development :: Libraries",
 ]
 keywords = ["accumarray", "aggregate", "groupby", "grouping", "indexing"]
-requires-python = ">=3.10"
+requires-python = ">=3.10" # 0.15 will raise this to ">=3.11"
 dependencies = ["numpy"]
 
 [project.optional-dependencies]