Allow boolean equal to define units

Author: cphyc

yt/data_objects/tests/test_add_field.py

@@ -243,6 +243,13 @@ def test_add_field_quick_syntax2():
         ds.r["gas", "temperature"] * ds.units.kb / ds.r["gas", "volume"],
     )
 
+    # Returning boolean
+    dx_min = ds.r["index", "dx"].min()
+    ds.fields.gas.smallest_cells = ds.fields.gas.dx == dx_min
+    np.testing.assert_allclose(
+        ds.r["gas", "smallest_cells"].value, (dx_min == ds.r["gas", "dx"])
+    )
+
 
 @pytest.fixture()
 def capturable_logger(caplog):

yt/fields/derived_field.py

@@ -115,19 +115,23 @@ def __geq__(self, other) -> "DerivedFieldCombination":
     def __gt__(self, other) -> "DerivedFieldCombination":
         return DerivedFieldCombination([self, other], op=operator.gt)
 
-    # def __eq__(self, other) -> "DerivedFieldCombination":
-    #     return DerivedFieldCombination([self, other], op=operator.eq)
+    def __eq__(self, other) -> "DerivedFieldCombination":
+        return DerivedFieldCombination([self, other], op=operator.eq)
 
     def __ne__(self, other) -> "DerivedFieldCombination":  # type: ignore[override]
         return DerivedFieldCombination([self, other], op=operator.ne)
 
+    @abc.abstractmethod
+    def __hash__(self) -> int:
+        pass
+
 
 class DerivedFieldCombination(DerivedFieldBase):
     sampling_type: str | None
     terms: list
-    op: Callable | None
+    op: Callable
 
-    def __init__(self, terms: list, op=None):
+    def __init__(self, terms: list, op: Callable):
         if not terms:
             raise ValueError("DerivedFieldCombination requires at least one term.")
 
@@ -146,6 +150,9 @@ def __init__(self, terms: list, op=None):
         self.terms = terms
         self.op = op
 
+    def __hash__(self):
+        return hash((self.sampling_type, tuple(self.terms), self.op))
+
     def __call__(self, field, data):
         """
         Return the value of the field in a given data object.
@@ -307,6 +314,26 @@ def __init__(
             self._shared_aliases_list = alias._shared_aliases_list
             self._shared_aliases_list.append(self)
 
+    def __hash__(self):
+        return hash(
+            (
+                self.name,
+                self.sampling_type,
+                self._function,
+                self.units,
+                self.take_log,
+                tuple(self.validators),
+                self.vector_field,
+                self.display_field,
+                self.not_in_all,
+                self.display_name,
+                self.output_units,
+                self.dimensions,
+                self.ds,
+                tuple(self.nodal_flag),
+            )
+        )
+
     def _copy_def(self):
         dd = {}
         dd["name"] = self.name