ArgsContainer: Add add_argument() function

add_argument() at the face of it looks much like
ArgumentParser.add_argument(), but is a function, not a class method.
It takes the ArgsContainer|ArgParser instance as first argument, then
decides what type it is, and proceeds to use this knowledge to decide
whether or not the argument to be added already has a definition.

Signed-off-by: Jan Lindemann <jan@janware.com>

tools/python/jwutils/ArgsContainer.py

@@ -1,5 +1,7 @@
 # -*- coding: utf-8 -*-
 
+import argparse
+
 from collections import OrderedDict
 
 from jwutils.log import *
@@ -60,3 +62,18 @@ class ArgsContainer: # export
             except:
                 pass
             slog(prio, f'{name}: {val}', caller=caller)
+
+def add_argument(p: argparse.ArgumentParser|ArgsContainer, name: str, *args, **kwargs): # export
+
+    key = name.strip('--').replace('-', '_')
+    if isinstance(p, ArgsContainer):
+        if key in p.keys():
+            return
+    elif isinstance(p, argparse.ArgumentParser):
+        for action in p._actions:
+            if key == action.dest:
+                return
+    else:
+        raise Exception('Unknown type {type(p)} of {p} passed to add_argument()')
+
+    p.add_argument(name, *args, **kwargs)