Fix TypeError for datetime dict keys with key-cleaning flags (fixes #550)

deepdiff/helper.py

@@ -475,7 +475,12 @@ def number_to_string(number: Any, significant_digits: int, number_format_notatio
     except KeyError:
         raise ValueError("number_format_notation got invalid value of {}. The valid values are 'f' and 'e'".format(number_format_notation)) from None
 
-    if not isinstance(number, numbers):  # type: ignore
+    if not isinstance(number, only_numbers):  # type: ignore
+        # `numbers` also includes datetime types (they are orderable), but those
+        # cannot be reduced to significant digits via round(); leave any
+        # non-numeric value (datetimes, dates, etc.) unchanged. Otherwise using
+        # e.g. a datetime as a dict key together with ignore_numeric_type_changes
+        # raised "TypeError: type datetime.datetime doesn't define __round__".
         return number
     elif isinstance(number, Decimal):
         with localcontext() as ctx:

tests/test_diff_datetime.py

@@ -123,3 +123,22 @@ def test_datetime_within_array_with_timezone_diff(self):
         assert not DeepDiff(d1, d2)
         assert not DeepDiff(d1, d2, ignore_order=True)
         assert not DeepDiff(d1, d2, truncate_datetime='second')
+
+    def test_datetime_dict_key_with_ignore_flags(self):
+        # Using a datetime/date as a dict key together with flags that clean the
+        # keys (ignore_numeric_type_changes / ignore_string_case /
+        # ignore_string_type_changes) used to raise
+        # "TypeError: type datetime.datetime doesn't define __round__ method"
+        # because the keys were routed through number_to_string, which only
+        # handles real numbers.
+        dt = datetime(2020, 5, 17, 22, 15)
+        assert not DeepDiff({dt: 10.0}, {dt: 10}, ignore_numeric_type_changes=True)
+        # date objects (no time component) too
+        assert not DeepDiff(
+            {date(2020, 5, 17): 10.0},
+            {date(2020, 5, 17): 10},
+            ignore_numeric_type_changes=True,
+        )
+        # the other key-cleaning flags must not raise either
+        assert not DeepDiff({dt: 1}, {dt: 1}, ignore_string_case=True)
+        assert not DeepDiff({dt: 1}, {dt: 1}, ignore_string_type_changes=True)