Show package version number on kanta CLI

kanta/__main__.py

@@ -6,6 +6,7 @@ import argparse
 import asyncio
 import contextlib
 import importlib
+import importlib.metadata
 import importlib.util
 import logging
 import sys
@@ -161,10 +162,26 @@ def _format_ts(dt) -> str:
     return dt.replace(tzinfo=None, microsecond=0).isoformat(sep=" ")
 
 
+def _package_version() -> str:
+    """Return the installed package version, or ``"unknown"`` from a source tree."""
+    try:
+        return importlib.metadata.version("kanta")
+    except importlib.metadata.PackageNotFoundError:
+        return "unknown"
+
+
 def _parse_args(argv: list[str] | None = None) -> argparse.Namespace:
     parser = argparse.ArgumentParser(
         prog="kanta",
-        description="Read a kantadb file and print each change record to the console.",
+        description=(
+            f"kanta {_package_version()} - read a kantadb file and print each"
+            " change record to the console."
+        ),
+    )
+    parser.add_argument(
+        "--version",
+        action="version",
+        version=f"%(prog)s {_package_version()}",
     )
     parser.add_argument(
         "file",

tests/test_cli.py

@@ -3,6 +3,8 @@
 import sys
 from datetime import UTC, datetime
 
+import pytest
+
 from kanta.__main__ import (
     _extra_import_paths,
     _format_ts,
@@ -131,6 +133,23 @@ def test_cli_strips_ansi_without_color_support(tmp_path, capsys, monkeypatch):
     assert "snapshot s0" in err
 
 
+def test_cli_version_on_help_and_version_flag(capsys):
+    """--help and --version print the installed package version."""
+    import importlib.metadata
+
+    version = importlib.metadata.version("kanta")
+
+    with pytest.raises(SystemExit) as help_exit:
+        main(["--help"])
+    assert help_exit.value.code == 0
+    assert f"kanta {version}" in capsys.readouterr().out
+
+    with pytest.raises(SystemExit) as version_exit:
+        main(["--version"])
+    assert version_exit.value.code == 0
+    assert capsys.readouterr().out.strip() == f"kanta {version}"
+
+
 def test_import_dotted_from_file_path(tmp_path):
     """--data can be a filesystem path with an optional colon-separated symbol."""
     module = tmp_path / "models.py"