fix(main) argparse 'extend" action on <py38

Author: ankostis

src/promnesia/__main__.py

@@ -5,7 +5,7 @@
 from typing import List, Tuple, Optional, Dict, Sequence, Iterable, Iterator, Union
 from pathlib import Path
 from datetime import datetime
-from .compat import check_call
+from .compat import check_call, register_argparse_extend_action_in_pre_py38
 from tempfile import TemporaryDirectory
 
 
@@ -292,6 +292,7 @@ def add_index_args(parser: argparse.ArgumentParser, default_config_path: PathIsh
         :param default_config_path:
             if not given, all :func:`demo_sources()` are run
         """
+        register_argparse_extend_action_in_pre_py38(parser)
         parser.add_argument('--config', type=Path, default=default_config_path, help='Config path')
         parser.add_argument('--dry', action='store_true', help="Dry run, won't touch the database, only print the results out")
         parser.add_argument(

src/promnesia/compat.py

@@ -11,17 +11,36 @@ def _fix(args: Paths) -> List[str]:
     assert not isinstance(args, str), args # just to prevent shell=True calls...
     return list(map(str, args))
 
+
+import argparse
+
+def register_argparse_extend_action_in_pre_py38(parser: argparse.ArgumentParser):
+    import sys
+
+    if sys.version_info < (3, 8):
+
+        class ExtendAction(argparse.Action):
+
+            def __call__(self, parser, namespace, values, option_string=None):
+                items = getattr(namespace, self.dest) or []
+                items.extend(values)
+                setattr(namespace, self.dest, items)
+
+
+        parser.register('action', 'extend', ExtendAction)
+
+
 import subprocess
 
 def run(args: Paths, **kwargs) -> subprocess.CompletedProcess:
     return subprocess.run(_fix(args), **kwargs)
 
 def check_call(args: Paths, **kwargs) -> None:
     subprocess.check_call(_fix(args), **kwargs)
-    
+
 def check_output(args: Paths, **kwargs) -> bytes:
     return subprocess.check_output(_fix(args), **kwargs)
-    
+
 def Popen(args: Paths, **kwargs) -> subprocess.Popen:
     return subprocess.Popen(_fix(args), **kwargs)