mypy-friendly compat functions handling

my/core/common.py

@@ -280,14 +280,24 @@ tzdatetime = datetime
 
 fromisoformat: Callable[[str], datetime]
 import sys
-if sys.version_info.minor >= 7:
+if sys.version_info[:2] >= (3, 7):
     # prevent mypy on py3.6 from complaining...
-    fromisoformat_real = datetime.fromisoformat # type: ignore[attr-defined]
+    fromisoformat_real = datetime.fromisoformat
     fromisoformat = fromisoformat_real
 else:
     from .py37 import fromisoformat
 
 
+if sys.version_info[:2] >= (3, 8):
+    from typing import Literal
+else:
+    if TYPE_CHECKING:
+        from typing_extensions import Literal
+    else:
+        # erm.. I guess as long as it's not crashing, whatever...
+        Literal = Union
+
+
 # TODO doctests?
 def isoparse(s: str) -> tzdatetime:
     """

my/time/tz/common.py

@@ -23,7 +23,7 @@ def default_policy() -> Policy:
         return cast(Policy, user_config.tz.policy)
     except Exception as e:
         # todo meh.. need to think how to do this more carefully
-        # rationale: do not mess with user's data until they want
+        # rationale: do not mess with user's data unless they want
         return 'keep'