Add the --version option to the CLI

fawltydeps/main.py

@@ -7,7 +7,7 @@
 from enum import Enum, auto
 from operator import attrgetter
 from pathlib import Path
-from typing import List, Optional, Set, TextIO
+from typing import List, Optional, Set, TextIO, no_type_check
 
 from fawltydeps import extract_imports
 from fawltydeps.check import compare_imports_to_dependencies
@@ -21,6 +21,12 @@
     UnusedDependency,
 )
 
+if sys.version_info >= (3, 8):
+    import importlib.metadata as importlib_metadata
+else:
+    import importlib_metadata
+
+
 logger = logging.getLogger(__name__)
 
 
@@ -33,6 +39,17 @@ class Action(Enum):
     REPORT_UNUSED = auto()
 
 
+@no_type_check
+def version() -> str:
+    """Returns the version of fawltydeps."""
+
+    # This function is extracted to allow annotation with `@no_type_check`.
+    # Using `#type: ignore` on the line below leads to an
+    # "unused type ignore comment" MyPy error in python's version 3.8 and
+    # higher.
+    return str(importlib_metadata.version("fawltydeps"))
+
+
 @dataclass
 class Analysis:
     """Result from FawltyDeps analysis, to be presented to the user."""
@@ -132,6 +149,13 @@ def main() -> int:
         const={Action.REPORT_UNDECLARED, Action.REPORT_UNUSED},
         help="Report both undeclared and unused dependencies",
     )
+    parser.add_argument(
+        "-V",
+        "--version",
+        action="version",
+        version=f"FawltyDeps v{version()}",
+        help=("Print the version number of FawltyDeps"),
+    )
     select_action.add_argument(
         "--check-undeclared",
         dest="actions",

pyproject.toml

@@ -32,6 +32,7 @@ fawltydeps = "fawltydeps.main:main"
 # These are the main dependencies for fawltydeps at runtime.
 # Do not add anything here that is only needed by CI/tests/linters/developers
 python = "^3.7.2"
+importlib_metadata = {version = "^5.0.0", python = "<3.8"}
 isort = "^5.10"
 tomli = {version = "^2.0.1", python = "<3.11"}
 typing-extensions = {version = "^4.4.0", python = "<3.8"}