Multiple subcommand settings without explicit subcommand is now a warning instead of exception.

Author: mauvilsa

CHANGELOG.rst

@@ -10,6 +10,15 @@ only be introduced in major versions with advance notice in the **Deprecated**
 section of releases.
 
 
+v3.19.0 (2021-??-??)
+--------------------
+
+Changed
+^^^^^^^
+- Multiple subcommand settings without explicit subcommand is now a warning
+  instead of exception.
+
+
 v3.18.0 (2021-08-18)
 --------------------
 

jsonargparse/actions.py

@@ -1,12 +1,13 @@
 """Collection of useful actions to define arguments."""
 
+import argparse
 import os
 import re
 import sys
+import warnings
 import yaml
-import argparse
-from typing import Callable, Tuple, Type, Union
 from argparse import Namespace, Action, SUPPRESS, _HelpAction, _SubParsersAction
+from typing import Callable, Tuple, Type, Union
 
 from .optionals import FilesCompleterMethod, get_config_read_mode
 from .typing import path_type
@@ -746,24 +747,30 @@ def get_subcommand(parser, cfg_dict:dict, prefix:str='', fail_no_subcommand:bool
             if isinstance(action, _ActionSubCommands):
                 break
 
-        # Get sub-command parser
+        # Get subcommand settings keys
         subcommand_keys = []
         for key in action.choices.keys():
             if any([k.startswith(prefix+key+'.') for k in cfg_dict.keys()]):
                 subcommand_keys.append(key)
 
+        # Get subcommand
         subcommand = None
         dest = prefix + action.dest
         if dest in cfg_dict and cfg_dict[dest] is not None:
             subcommand = cfg_dict[dest]
+        elif len(subcommand_keys) > 0:
+            cfg_dict[dest] = subcommand = subcommand_keys[0]
+            if len(subcommand_keys) > 1:
+                warnings.warn(
+                    'Multiple subcommand settings provided (' + ', '.join(subcommand_keys) + ') without an explicit "' +
+                    dest + '" key. Subcommand "' + subcommand + '" will be used.'
+                )
+
+        # Remove extra subcommand settings
+        if subcommand and len(subcommand_keys) > 1:
             for key in [k for k in subcommand_keys if k != subcommand]:
                 for subkey in [k for k in cfg_dict.keys() if k.startswith(prefix+key+'.')]:
                     del cfg_dict[subkey]
-        else:
-            if len(subcommand_keys) > 1:
-                raise KeyError('Key "'+dest+'" is required if multiple sub-command values are provided: '+str(subcommand_keys)+'.')
-            elif len(subcommand_keys) == 1:
-                cfg_dict[dest] = subcommand = subcommand_keys[0]
 
         if subcommand is None and not (fail_no_subcommand and action._required):
             return None, None

jsonargparse_tests/core_tests.py

@@ -1,9 +1,9 @@
 #!/usr/bin/env python3
 
-import sys
 import json
-import yaml
 import platform
+import warnings
+import yaml
 from io import StringIO
 from contextlib import redirect_stdout
 from collections import OrderedDict
@@ -361,9 +361,19 @@ def test_subcommands(self):
         self.assertEqual(cfg['subcommand'], 'a')
         self.assertEqual(strip_meta(cfg['a']), {'ap1': 'ap1_cfg', 'ao1': 'ao1_def'})
         self.assertRaises(ParserError, lambda: parser.parse_string('{"a": {"ap1": "ap1_cfg", "unk": "unk_cfg"}}'))
-        self.assertRaises(ParserError, lambda: parser.parse_string('{"a": {"ap1": "ap1_cfg"}, "b": {"nums": {"val1": 2}}}'))
 
-        cfg = parser.parse_string('{"subcommand": "a", "a": {"ap1": "ap1_cfg"}, "b": {"nums": {"val1": 2}}}')
+        with warnings.catch_warnings(record=True) as w:
+            warnings.simplefilter("always")
+            cfg = parser.parse_string('{"a": {"ap1": "ap1_cfg"}, "b": {"nums": {"val1": 2}}}')
+            self.assertEqual(cfg.subcommand, 'a')
+            self.assertFalse(hasattr(cfg, 'b'))
+            self.assertEqual(len(w), 1)
+            self.assertIn('Subcommand "a" will be used', str(w[0].message))
+
+        cfg = parser.parse_string('{"subcommand": "b", "a": {"ap1": "ap1_cfg"}, "b": {"nums": {"val1": 2}}}')
+        self.assertFalse(hasattr(cfg, 'a'))
+
+        cfg = parser.parse_args(['--cfg={"a": {"ap1": "ap1_cfg"}, "b": {"nums": {"val1": 2}}}', 'a'])
         self.assertFalse(hasattr(cfg, 'b'))
 
         os.environ['APP_O1'] = 'o1_env'

setup.cfg

@@ -63,7 +63,7 @@ long_description_content_type = text/x-rst
 author = Mauricio Villegas
 author_email = [email protected]
 license = MIT
-url = https://omni-us.github.io/jsonargparse
+url = https://github.com/omni-us/jsonargparse
 project_urls =
     Documentation-stable = https://jsonargparse.readthedocs.io/en/stable/
     Documentation-latest = https://jsonargparse.readthedocs.io/en/latest/