suggestion from code review

firedrake/assemble.py

@@ -143,20 +143,18 @@ def get_assembler(form, *args, **kwargs):
 
     """
     is_base_form_preprocessed = kwargs.pop('is_base_form_preprocessed', False)
-    bcs = kwargs.get('bcs', None)
-    fc_params = kwargs.get('form_compiler_parameters', None)
     if isinstance(form, ufl.form.BaseForm) and not is_base_form_preprocessed:
         mat_type = kwargs.get('mat_type', None)
+        fc_params = kwargs.get('form_compiler_parameters', None)
         # Preprocess the DAG and restructure the DAG
         # Only pre-process `form` once beforehand to avoid pre-processing for each assembly call
         form = BaseFormAssembler.preprocess_base_form(form, mat_type=mat_type, form_compiler_parameters=fc_params)
     if isinstance(form, (ufl.form.Form, slate.TensorBase)) and not BaseFormAssembler.base_form_operands(form):
         diagonal = kwargs.pop('diagonal', False)
         if len(form.arguments()) == 0:
-            return ZeroFormAssembler(form, form_compiler_parameters=fc_params)
+            return ZeroFormAssembler(form, **kwargs)
         elif len(form.arguments()) == 1 or diagonal:
-            return OneFormAssembler(form, *args, bcs=bcs, form_compiler_parameters=fc_params, needs_zeroing=kwargs.get('needs_zeroing', True),
-                                    zero_bc_nodes=kwargs.get('zero_bc_nodes', True), diagonal=diagonal)
+            return OneFormAssembler(form, *args, diagonal=diagonal, **kwargs)
         elif len(form.arguments()) == 2:
             return TwoFormAssembler(form, *args, **kwargs)
         else:
@@ -1149,13 +1147,13 @@ class OneFormAssembler(ParloopFormAssembler):
 
     @classmethod
     def _cache_key(cls, form, bcs=None, form_compiler_parameters=None, needs_zeroing=True,
-                   zero_bc_nodes=False, diagonal=False, weight=1.0):
+                   zero_bc_nodes=True, diagonal=False, weight=1.0):
         bcs = solving._extract_bcs(bcs)
-        return tuple(bcs), tuplify(form_compiler_parameters), needs_zeroing, zero_bc_nodes, diagonal
+        return tuple(bcs), tuplify(form_compiler_parameters), needs_zeroing, zero_bc_nodes, diagonal, weight
 
     @FormAssembler._skip_if_initialised
     def __init__(self, form, bcs=None, form_compiler_parameters=None, needs_zeroing=True,
-                 zero_bc_nodes=False, diagonal=False, weight=1.0):
+                 zero_bc_nodes=True, diagonal=False, weight=1.0):
         super().__init__(form, bcs=bcs, form_compiler_parameters=form_compiler_parameters, needs_zeroing=needs_zeroing)
         self._weight = weight
         self._diagonal = diagonal