Update get_arg_list_as_str to skip func params

This patch updates inspect_utils.get_arg_list_as_str
so that it skips handling parameters that can't be
JSON serialized. One example of this would be a function
parameter (func=time.sleep). Some of the OpenStack
clients have functions that would be useful to expose
by simply relying on the default settings for these
parameters.

Change-Id: Id1cc8e79db3001ffec5066b2e81ec2e5119e875a
Closes-bug: #1584366

mistral/tests/unit/utils/test_inspect_utils.py

@@ -12,6 +12,8 @@
 #    See the License for the specific language governing permissions and
 #    limitations under the License.
 
+import time
+
 from mistral.actions import std_actions
 from mistral.tests.unit import base
 from mistral.utils import inspect_utils as i_u
@@ -37,3 +39,11 @@ class InspectUtilsTest(base.BaseTest):
         parameters_str = i_u.get_arg_list_as_str(clazz.__init__)
 
         self.assertEqual("wf_ex, task_spec, ctx", parameters_str)
+
+    def test_get_parameters_str_with_function_parameter(self):
+
+        def test_func(foo, bar=None, test_func=time.sleep):
+            pass
+
+        parameters_str = i_u.get_arg_list_as_str(test_func)
+        self.assertEqual("foo, bar=null", parameters_str)

mistral/utils/inspect_utils.py

@@ -66,12 +66,15 @@ def get_arg_list_as_str(func):
 
     for index, default in enumerate(args):
         if index >= diff_args_defs:
+            try:
                 arg_str_list.append(
                     "%s=%s" % (
                         args[index],
                         json.dumps(defs[index - diff_args_defs])
                     )
                 )
+            except TypeError:
+                pass
         else:
             arg_str_list.append("%s" % args[index])