feat: add defaults argument

src/defopt.py

@@ -243,6 +243,7 @@ def run(
     argparse_kwargs: dict = {},
     intermixed: bool = False,
     argv: Optional[List[str]] = None,
+    defaults: Optional[Dict[str, Any]] = None
 ):
     """
     Process command-line arguments and run the given functions.
@@ -302,20 +303,26 @@ def run(
         listed in the `argparse` documentation.
     :param argv:
         Command line arguments to parse (default: ``sys.argv[1:]``).
+    :param defaults:
+        Mapping for argument defaults passed to
+        `~argparse.ArgumentParser.set_defaults`.  Key must be the command name,
+        value is a mapping of argument name to default value.
     :return:
         The value returned by the function that was run.
     """
     return bind(
         funcs, parsers=parsers, short=short, cli_options=cli_options,
         show_defaults=show_defaults, show_types=show_types,
         no_negated_flags=no_negated_flags, version=version,
-        argparse_kwargs=argparse_kwargs, intermixed=intermixed, argv=argv)()
+        argparse_kwargs=argparse_kwargs, intermixed=intermixed, argv=argv,
+        defaults=defaults)()
 
 
 _DefoptOptions = namedtuple(
     '_DefoptOptions',
     ['parsers', 'short', 'cli_options', 'show_defaults', 'show_types',
-     'no_negated_flags', 'version', 'argparse_kwargs', 'intermixed', 'argv'])
+     'no_negated_flags', 'version', 'argparse_kwargs', 'intermixed', 'argv',
+     'defaults'])
 
 
 def _options(**kwargs):
@@ -359,12 +366,17 @@ def _create_parser(funcs, opts):
                                **opts.argparse_kwargs})
     version_sources = []
     if callable(funcs):
-        _populate_parser(funcs, parser, opts)
+        _populate_parser(funcs, parser, opts, opts.defaults)
         version_sources.append(funcs)
     else:
         subparsers = parser.add_subparsers()
         for func, subparser in _recurse_functions(funcs, subparsers):
-            _populate_parser(func, subparser, opts)
+            # FIXME: need fully qualitified name for nested commands...
+            defaults = None if opts.defaults is None else opts.defaults.get(
+                func.__name__,
+                opts.defaults.get(func.__name__.replace('_', '-'), None)
+            )
+            _populate_parser(func, subparser, opts, defaults)
             version_sources.append(func)
     if isinstance(opts.version, str):
         version_string = opts.version
@@ -563,7 +575,7 @@ def _get_type_from_hint(hint):
     return hint
 
 
-def _populate_parser(func, parser, opts):
+def _populate_parser(func, parser, opts, defaults):
     sig = signature(func)
     parser.description = sig.doc
 
@@ -605,6 +617,11 @@ def _populate_parser(func, parser, opts):
             raise ValueError(f'no type found for parameter {name}')
         hasdefault = param.default is not param.empty
         default = param.default if hasdefault else SUPPRESS
+
+        if not hasdefault and defaults is not None and name in defaults:
+            hasdefault = True
+            default = defaults[name]
+
         required = not hasdefault and param.kind != param.VAR_POSITIONAL
         positional = name in positionals