Parses module in more robust way for fn gathering

inspect.getmodule(fn) depends on the state of sys.modules. This can
break if you're doing repeated parsing -- E.G. running it then wiping
sys.modules. Instead, we can just ask the function for its module. It's
simpler, and won't break.

hamilton/graph_utils.py

@@ -3,8 +3,8 @@
 from typing import Callable, List, Tuple
 
 
-def is_submodule(child: ModuleType, parent: ModuleType):
-    return parent.__name__ in child.__name__
+def is_submodule(child: str, parent: str):
+    return parent in child
 
 
 def find_functions(function_module: ModuleType) -> List[Tuple[str, Callable]]:
@@ -18,7 +18,7 @@ def valid_fn(fn):
         return (
             inspect.isfunction(fn)
             and not fn.__name__.startswith("_")
-            and is_submodule(inspect.getmodule(fn), function_module)
+            and is_submodule(fn.__module__, function_module.__name__)
         )
 
     return [f for f in inspect.getmembers(function_module, predicate=valid_fn)]