command: add optional shell completion support using argcomplete

Author: scop

README.md

@@ -18,7 +18,8 @@ content is hashed. If it does, only content of the first capturing
 group is.
 
 The command line tool operates as a pipe, reading standard input and
-outputting to standard output.
+outputting to standard output. It has optional shell completion support
+using [argcomplete](https://pypi.org/project/argcomplete/).
 
 ## Examples
 

bin/hashpipe

@@ -1,4 +1,5 @@
 #!/usr/bin/python3 -u
+# PYTHON_ARGCOMPLETE_OK
 
 """Hashpipe entry point."""
 

hashpipe/__init__.py

@@ -145,14 +145,16 @@ def main(
         help="Prefix to add in replacements",
     )
 
-    parser.add_argument(
+    algorithm_arg = parser.add_argument(
         "-a",
         "--algorithm",
         type=str,
         default=DEFAULT_ALGORITHM,
         help="Digest algorithm to use, one of: %s"
         % ", ".join(sorted(_available_algorithms(), key=lambda x: x.lower())),
     )
+    # type ignore: argcomplete adds the "completer" attribute
+    algorithm_arg.completer = lambda **_: _available_algorithms()  # type: ignore
 
     parser.add_argument(
         "-A",
@@ -175,6 +177,13 @@ def pattern(arg: str) -> Pattern[bytes]:
             "regex", type=pattern, metavar="REGEX", help="Regular expression to match"
         )
 
+    try:
+        import argcomplete  # type: ignore # pylint: disable=import-outside-toplevel
+    except ImportError:
+        pass
+    else:
+        argcomplete.autocomplete(parser)
+
     args = parser.parse_args()
 
     if args.available_algorithms:

setup.cfg

@@ -27,6 +27,10 @@ tests_require =
 packages = hashpipe
 scripts = bin/hashpipe
 
+[options.extras_require]
+completion =
+    argcomplete
+
 [options.package_data]
 hashpipe =
     py.typed