use one line boolean condition with add types

rest_framework/utils/timezone.py

@@ -1,15 +1,15 @@
 from datetime import datetime, timezone, tzinfo
 
 
-def datetime_exists(dt):
+def datetime_exists(dt: datetime) -> bool:
     """Check if a datetime exists. Taken from: https://pytz-deprecation-shim.readthedocs.io/en/latest/migration.html"""
     # There are no non-existent times in UTC, and comparisons between
     # aware time zones always compare absolute times; if a datetime is
     # not equal to the same datetime represented in UTC, it is imaginary.
     return dt.astimezone(timezone.utc) == dt
 
 
-def datetime_ambiguous(dt: datetime):
+def datetime_ambiguous(dt: datetime) -> bool:
     """Check whether a datetime is ambiguous. Taken from: https://pytz-deprecation-shim.readthedocs.io/en/latest/migration.html"""
     # If a datetime exists and its UTC offset changes in response to
     # changing `fold`, it is ambiguous in the zone specified.
@@ -18,8 +18,6 @@ def datetime_ambiguous(dt: datetime):
     )
 
 
-def valid_datetime(dt):
+def valid_datetime(dt: datetime) -> bool:
     """Returns True if the datetime is not ambiguous or imaginary, False otherwise."""
-    if isinstance(dt.tzinfo, tzinfo) and not datetime_ambiguous(dt):
-        return True
-    return False
+    return isinstance(dt.tzinfo, tzinfo) and not datetime_ambiguous(dt)