tags: add python_tag

docs/tags.rst

@@ -46,6 +46,8 @@ items that applications should need to reference, in order to parse and check ta
 
 .. autofunction:: sys_tags
 
+.. autofunction:: python_tag
+
 .. autofunction:: create_compatible_tags_selector
 
 .. autoexception:: TooManyTagsError

src/packaging/tags.py

@@ -46,6 +46,7 @@
     "mac_platforms",
     "parse_tag",
     "platform_tags",
+    "python_tag",
     "sys_tags",
 ]
 
@@ -910,6 +911,28 @@ def _version_nodot(version: PythonVersion) -> str:
     return "".join(map(str, version))
 
 
+def python_tag(
+    *, implementation: bool = True, version: bool = True, warn: bool = False
+) -> str:
+    """
+    Returns a :pep:`425` python tag for the running interpreter.
+
+    :param bool implementation: Whether the tag should be specific to the
+        running interpreter (e.g. ``cp311`` or ``pp311``) instead of using the
+        generic ``py`` prefix (e.g. ``py311``). Defaults to ``True``.
+    :param bool version: Whether the tag should include the full interpreter
+        version (e.g. ``cp311``) instead of only the major version
+        (e.g. ``cp3``). Defaults to ``True``.
+    :param bool warn: Whether warnings should be logged. Defaults to ``False``.
+
+    .. versionadded:: 26.3
+    """
+    prefix = interpreter_name() if implementation else "py"
+    if version:
+        return prefix + interpreter_version(warn=warn)
+    return prefix + str(sys.version_info.major)
+
+
 def sys_tags(*, warn: bool = False) -> Iterator[Tag]:
     """
     Yields the sequence of tag triples that the running interpreter supports.
@@ -949,9 +972,9 @@ def sys_tags(*, warn: bool = False) -> Iterator[Tag]:
         yield from generic_tags(warn=warn)
 
     if interp_name == "pp":
-        interp = "pp3"
+        interp = python_tag(version=False)
     elif interp_name == "cp":
-        interp = "cp" + interpreter_version(warn=warn)
+        interp = python_tag(warn=warn)
     else:
         interp = None
     yield from compatible_tags(interpreter=interp)

tests/test_tags.py

@@ -304,6 +304,44 @@ def test_sys_version_info(
         assert tags.interpreter_version() == version_str
 
 
+class TestPythonTag:
+    @pytest.mark.parametrize(
+        ("implementation", "version", "expected"),
+        [
+            (True, True, "cp311"),
+            (True, False, "cp3"),
+            (False, True, "py311"),
+            (False, False, "py3"),
+        ],
+    )
+    def test_python_tag_cpython(
+        self,
+        implementation: bool,
+        version: bool,
+        expected: str,
+        monkeypatch: pytest.MonkeyPatch,
+    ) -> None:
+        monkeypatch.setattr(tags, "interpreter_name", lambda: "cp")
+        monkeypatch.setattr(tags, "interpreter_version", lambda **kwargs: "311")
+        assert (
+            tags.python_tag(implementation=implementation, version=version) == expected
+        )
+
+    def test_python_tag_pypy(self, monkeypatch: pytest.MonkeyPatch) -> None:
+        monkeypatch.setattr(tags, "interpreter_name", lambda: "pp")
+        monkeypatch.setattr(tags, "interpreter_version", lambda **kwargs: "311")
+        assert tags.python_tag() == "pp311"
+        assert tags.python_tag(version=False) == "pp3"
+
+    def test_python_tag_other_interpreter(
+        self, monkeypatch: pytest.MonkeyPatch
+    ) -> None:
+        monkeypatch.setattr(tags, "interpreter_name", lambda: "graalpy")
+        monkeypatch.setattr(tags, "interpreter_version", lambda **kwargs: "311")
+        assert tags.python_tag() == "graalpy311"
+        assert tags.python_tag(implementation=False) == "py311"
+
+
 class TestMacOSPlatforms:
     @pytest.mark.parametrize(
         ("arch", "is_32bit", "expected"),