Fixed bug in handle_py3_kw_only_args

- Fixed a few bugs in initial implementation, added unit test.
- Fixed some very minor doc issue.

.gitignore

@@ -11,6 +11,7 @@ zdist/
 build.cache
 .release_name
 .release_path
+docs/source/_build/
 
 # Byte-compiled / optimized / DLL files
 __pycache__/
@@ -113,4 +114,3 @@ ENV/
 
 # mypy
 .mypy_cache/
-zdist/

ksconf/builder/__init__.py

@@ -90,7 +90,7 @@ def run(self, executable, *args, **kw_only):
         The process will run withing the working directory of the build folder.
 
         :param str executable: Executable to launch for a build step.
-        :param str *args: Additional arguments for the new process.
+        :param str args: Additional argument(s) for the new process.
         :param str cwd:  Optional kw arg to change the working directory.  This
                          defaults to the build folder.
         """

ksconf/util/__init__.py

@@ -65,32 +65,42 @@ def debug_traceback():  # pragma: no cover
             traceback.print_exc(level)
 
 
-def handle_py3_kw_only_args(kw, *args):
+def handle_py3_kw_only_args(kw, *default_args):
     """ Python 2.7 workaround for Python 3 style kw arg after '*' arg.
 
     Example Python 3 syntax:
 
     ..  code-block:: py
 
-        def f(arg, *args, a=True, b=False): ...
+        def f(arg, *args, a=True, b=False):
+            ...
 
-    Example Python 2 syntax:
+    Example Python 2 syntax with this helper function:
 
     ..  code-block:: py
 
         def f(arg, *args, **kw_only):
             a, b = handle_py3_kw_only_args(kw_only, ("a", True), ("b", False))
+            ...
+
+    :param dict kw: keyword arguments provided to the calling function. Be aware
+                    that this dict will be empty after this function is done.
+    :param tuple default_args: pairs of keyword argument to the caller function
+                               in argument (arg_name, default_value) order.
+    :raises TypeError: if ``kw`` contains any keys not defined in ``args``
+                       This mirrors Python's native behavior when an unexpected
+                       argument is passed to a function.
     """
     out = []
-    for arg_name, arg_default in args:
-        if arg_name in kw:
+    for arg_name, arg_default in default_args:
+        try:
             out.append(kw.pop(arg_name))
-        else:
+        except KeyError:
             out.append(arg_default)
-    if args:
+    if kw:
         import inspect
         caller = inspect.currentframe().f_back.f_code.co_name
         # Should all unexpected args be reported?  feels like this good enough
         raise TypeError("{} got an unexpected keyword argument '{}'"
-                        .format(caller, args.keys()[0]))
+                        .format(caller, list(kw)[0]))
     return out

tests/test_util.py

@@ -24,6 +24,19 @@ def test_bwlist(self):
         self.assertTrue(match_bwlist("hotdog", bwlist))
         self.assertTrue(match_bwlist("bake", bwlist))
 
+    def test_handle_p3koa(self):
+        from ksconf.util import handle_py3_kw_only_args
+        kw = {"a": 1, "b": 2}
+        a, b, c = handle_py3_kw_only_args(kw, ("a", None), ("b", 3), ("c", 99))
+        self.assertEqual(a, 1)
+        self.assertEqual(b, 2)
+        self.assertEqual(c, 99)
+
+        # Should raise 'unexpected argument' here because 'a' is not defined
+        kw = {a: 1}
+        with self.assertRaises(TypeError):
+            c = handle_py3_kw_only_args(kw, ("c", 99))
+
 
 class KsconfMiscIternalsTest(unittest.TestCase):