core.stats: fix is_data_provider when from __future__ import annotations is used

my/core/stats.py

@@ -4,7 +4,6 @@ Helpers for hpi doctor/stats functionality.
 import collections
 import importlib
 import inspect
-import sys
 import typing
 from typing import Optional, Callable, Any, Iterator, Sequence, Dict, List
 
@@ -59,7 +58,14 @@ def is_data_provider(fun: Any) -> bool:
         if fun.__name__ == 'inputs' or fun.__name__.endswith('_inputs'):
             return False
 
-    return_type = sig.return_annotation
+    # inspect.signature might return str instead of a proper type object
+    # if from __future__ import annotations is used
+    # so best to rely on get_type_hints (which evals the annotations)
+    type_hints = typing.get_type_hints(fun)
+    return_type = type_hints.get('return')
+    if return_type is None:
+        return False
+
     return type_is_iterable(return_type)
 
 
@@ -123,9 +129,6 @@ def test_sig_required_params() -> None:
 
 
 def type_is_iterable(type_spec) -> bool:
-    if sys.version_info[1] < 8:
-        # there is no get_origin before 3.8, and retrofitting gonna be a lot of pain
-        return any(x in str(type_spec) for x in ['List', 'Sequence', 'Iterable', 'Iterator'])
     origin = typing.get_origin(type_spec)
     if origin is None:
         return False