Add function to determine if module is dynamic

_is_dynamic_module returns True if the specified module is in the set
of modules that should be considered dynamic for pickling purposes. If
submodules is True, then the module's parent modules will be searched
to see if they were registered as dynamic.

cloudpickle/cloudpickle.py

@@ -137,6 +137,21 @@ def unregister_dynamic_module(module):
     _CUSTOM_DYNAMIC_MODULES_BY_NAME.remove(module_name)
 
 
+def _is_dynamic_module(module, submodules=True):
+    module_name = module.__name__ if inspect.ismodule(module) else module
+    if module_name in _CUSTOM_DYNAMIC_MODULES_BY_NAME:
+        return True
+    if submodules:
+        while True:
+            parent_name = module_name.rsplit(".", 1)[0]
+            if parent_name == module_name:
+                break
+            if parent_name in _CUSTOM_DYNAMIC_MODULES_BY_NAME:
+                return True
+            module_name = parent_name
+    return False
+
+
 def _whichmodule(obj, name):
     """Find the module an object belongs to.