feat(mf6): opt out of writing default values

autotest/test_mf6_optional_default_value.py

@@ -0,0 +1,86 @@
+"""
+Test that optional package variables with default values aren't written to
+input files when write_defaults=False.
+
+Reproduces https://github.com/modflowpy/flopy/issues/2710.
+"""
+
+from pathlib import Path
+
+import pytest
+
+import flopy
+
+pytestmark = pytest.mark.mf6
+
+
+def _build_prt_sim(ws, coordinate_check_method="eager"):
+    sim = flopy.mf6.MFSimulation(sim_name="prt", sim_ws=str(ws))
+    flopy.mf6.ModflowTdis(sim, nper=1, perioddata=[(1.0, 1, 1.0)])
+    ems = flopy.mf6.ModflowEms(sim)
+    prt = flopy.mf6.ModflowPrt(sim, modelname="prt")
+    flopy.mf6.ModflowPrtdis(
+        prt,
+        nlay=1,
+        nrow=1,
+        ncol=3,
+        delr=1.0,
+        delc=1.0,
+        top=1.0,
+        botm=0.0,
+    )
+    flopy.mf6.ModflowPrtmip(prt, porosity=0.1)
+    flopy.mf6.ModflowPrtprp(
+        prt,
+        nreleasepts=1,
+        packagedata=[(0, (0, 0, 0), 0.5, 0.5, 0.5)],
+        perioddata={0: ["FIRST"]},
+        coordinate_check_method=coordinate_check_method,
+    )
+    flopy.mf6.ModflowPrtoc(prt, track_filerecord=[("prt.trk",)])
+    sim.register_solution_package(ems, [prt.name])
+    return sim
+
+
+def _prp_text(ws):
+    prp_files = list(Path(ws).glob("*.prp"))
+    assert len(prp_files) == 1, f"expected one .prp file, found: {prp_files}"
+    return prp_files[0].read_text().upper()
+
+
+def test_coordinate_check_method(function_tmpdir):
+    # write_defaults=True, default value
+    ws = Path(function_tmpdir) / "write_defaults"
+    ws.mkdir()
+    sim = _build_prt_sim(ws, coordinate_check_method="eager")
+    sim.write_simulation()
+    text = _prp_text(ws)
+    assert "COORDINATE_CHECK_METHOD" in text
+    assert "EAGER" in text
+
+    # write_defaults=False, default value
+    ws = Path(function_tmpdir) / "eager"
+    ws.mkdir()
+    sim = _build_prt_sim(ws, coordinate_check_method="eager")
+    sim.simulation_data.write_defaults = False
+    sim.write_simulation()
+    assert "COORDINATE_CHECK_METHOD" not in _prp_text(ws)
+
+    # write_defaults=False, non-default value
+    ws = Path(function_tmpdir) / "none"
+    ws.mkdir()
+    sim = _build_prt_sim(ws, coordinate_check_method="none")
+    sim.simulation_data.write_defaults = False
+    sim.write_simulation()
+    text = _prp_text(ws)
+    assert "COORDINATE_CHECK_METHOD" in text
+    assert "NONE" in text
+
+    # write_defaults=False passed directly to write_simulation(), default
+    # value, overriding simulation_data.write_defaults for this call only
+    ws = Path(function_tmpdir) / "write_simulation_kwarg"
+    ws.mkdir()
+    sim = _build_prt_sim(ws, coordinate_check_method="eager")
+    sim.write_simulation(write_defaults=False)
+    assert "COORDINATE_CHECK_METHOD" not in _prp_text(ws)
+    assert sim.simulation_data.write_defaults is True

flopy/mf6/data/mfdatascalar.py

@@ -318,6 +318,28 @@ def add_one(self):
                 self._simulation_data.debug,
             )
 
+    @staticmethod
+    def _matches_default(data_item, current):
+        # only compare scalar types. composite types are always written
+        if data_item.type == DatumType.integer:
+            try:
+                return int(float(current)) == int(float(data_item.default_value))
+            except (ValueError, TypeError):
+                return False
+        elif data_item.type == DatumType.double_precision:
+            try:
+                return float(current) == float(data_item.default_value)
+            except (ValueError, TypeError):
+                return False
+        elif data_item.type == DatumType.string:
+            return (
+                str(current).lower().strip()
+                == data_item.default_value.lower().strip()
+            )
+        elif data_item.type == DatumType.keyword:
+            return data_item.default_value.lower().strip() == "true"
+        return False
+
     def get_file_entry(
         self,
         values_only=False,
@@ -361,6 +383,12 @@ def get_file_entry(
                 self._simulation_data.debug,
                 ex,
             )
+        if self.structure.optional and not self._simulation_data.write_defaults:
+            data_item = self.structure.data_item_structures[0]
+            if data_item.default_value is not None and self._matches_default(
+                data_item, storage.get_data()
+            ):
+                return ""
         if (
             self.structure.type == DatumType.keyword
             or self.structure.type == DatumType.record

flopy/mf6/data/mfstructure.py

@@ -617,7 +617,7 @@ def set_value(self, line, common):
                     self.ucase = bool(arr_line[1])
             elif arr_line[0] == "preserve_case":
                 self.preserve_case = self._get_boolean_val(arr_line)
-            elif arr_line[0] == "default_value":
+            elif arr_line[0] in ("default_value", "default"):
                 self.default_value = " ".join(arr_line[1:])
             elif arr_line[0] == "numeric_index":
                 self.numeric_index = self._get_boolean_val(arr_line)

flopy/mf6/mfsimbase.py

@@ -259,6 +259,7 @@ def __init__(self, path: Union[str, PathLike], mfsim):
         self._verbosity_level = VerbosityLevel.normal
         self._max_columns_set_by = None  # Can be None, 'user', or 'auto'
         self.use_pandas = True
+        self.write_defaults = True
 
         self._update_str_format()
 
@@ -1717,7 +1718,10 @@ def set_all_data_internal(self, check_data=True):
             package.set_all_data_internal(check_data)
 
     def write_simulation(
-        self, ext_file_action=ExtFileAction.copy_relative_paths, silent=False
+        self,
+        ext_file_action=ExtFileAction.copy_relative_paths,
+        silent=False,
+        write_defaults=None,
     ):
         """
         Write the simulation to files.
@@ -1730,10 +1734,23 @@ def write_simulation(
                 by absolute paths fixed.
             silent : bool
                 Writes out the simulation in silent mode (verbosity_level = 0)
+            write_defaults : bool
+                Whether to write optional variables whose value equals the
+                MODFLOW 6 default for that variable. Defaults to None, which
+                defers to simulation_data.write_defaults (True unless changed
+                by the user). Set to False to omit such variables from the
+                input files, which can be useful when a MODFLOW 6 version
+                does not yet support an option flopy otherwise writes by
+                default.
 
         """
         self._auto_set_max_columns()
 
+        sim_data = self.simulation_data
+        if write_defaults is not None:
+            saved_write_defaults = sim_data.write_defaults
+            sim_data.write_defaults = write_defaults
+
         saved_verb_lvl = self.simulation_data.verbosity_level
         if silent:
             self.simulation_data.verbosity_level = VerbosityLevel.quiet
@@ -1795,6 +1812,8 @@ def write_simulation(
 
         if silent:
             self.simulation_data.verbosity_level = saved_verb_lvl
+        if write_defaults is not None:
+            sim_data.write_defaults = saved_write_defaults
 
     def set_sim_path(self, path: Union[str, PathLike]):
         """Return a list of output data keys.