fix(mp7): fix input file writing (#2679)

Util2d assumes its first argument is a model, but a ParticleGroup was being passed. This caused an error when writing MP7 input files with certain release configurations. Don't pass ParticleGroup to Util2d as it's not needed, and only check self.model in Util2d if it's not None. Likewise in the ArrayFormat class.

Author: wpbonelli

autotest/test_particlegroup.py

@@ -1,3 +1,6 @@
+import tempfile
+from pathlib import Path
+
 import numpy as np
 
 from flopy.modpath import ParticleData, ParticleGroup
@@ -51,3 +54,57 @@ def test_pgroup_release_data():
         f"mp7: pgroup with releaseoption 3 returned "
         f"len(releasetimes)={len(pgrd3.releasetimes)}. Should be {nripg3}"
     )
+
+
+def test_pgroup_write_with_release_timing():
+    """Test that particle groups can be written to files with all release options."""
+    # create particles
+    partlocs = []
+    partids = []
+    nrow = 21
+    for i in range(nrow):
+        partlocs.append((0, i, 2))
+        partids.append(i)
+    pdata = ParticleData(partlocs, structured=True, particleids=partids)
+
+    with tempfile.TemporaryDirectory() as tmpdir:
+        tmpdir = Path(tmpdir)
+
+        # Test releaseoption 1 (single release time)
+        pgrd1 = ParticleGroup(
+            particlegroupname="PG1",
+            particledata=pdata,
+            filename=None,  # Write internally to test that path
+            releasedata=0.0,
+        )
+
+        # Test releaseoption 2 (time range with interval)
+        nripg2 = 10
+        ripg2 = 1.0
+        pgrd2 = ParticleGroup(
+            particlegroupname="PG2",
+            particledata=pdata,
+            filename=None,
+            releasedata=[nripg2, 0.0, ripg2],
+        )
+
+        # Test releaseoption 3 (explicit list of times).
+        # this triggers Util2d with None model
+        nripg3 = 7
+        pgrd3 = ParticleGroup(
+            particlegroupname="PG3",
+            particledata=pdata,
+            filename=None,
+            releasedata=[nripg3, np.array([0.0, 1.0, 1.2, 1.4, 1.6, 1.8, 2.0])],
+        )
+
+        # Write each particle group to test all release options
+        for pg in [pgrd1, pgrd2, pgrd3]:
+            sim_file = tmpdir / f"{pg.particlegroupname}_test.sim"
+            with open(sim_file, "w") as f:
+                # This should not raise an AttributeError
+                pg.write(f, ws=str(tmpdir))
+
+            # Verify file was created and has content
+            assert sim_file.exists()
+            assert sim_file.stat().st_size > 0

flopy/modpath/mp7particlegroup.py

@@ -149,7 +149,7 @@ def write(self, fp=None, ws="."):
             fp.write(f"{self.releasetimecount}\n")
             # item 31
             tp = self.releasetimes
-            v = Util2d(self, (tp.shape[0],), np.float32, tp, name="temp", locat=0)
+            v = Util2d(None, (tp.shape[0],), np.float32, tp, name="temp", locat=0)
             fp.write(v.string)
 
         # item 32

flopy/utils/util_array.py

@@ -89,8 +89,11 @@ def __init__(self, u2d, python=None, fortran=None, array_free_format=None):
         self._decimal = None
         if array_free_format is not None:
             self._freeformat_model = bool(array_free_format)
-        else:
+        elif u2d.model is not None:
             self._freeformat_model = bool(u2d.model.array_free_format)
+        else:
+            # Default to free format when no model is available
+            self._freeformat_model = True
 
         self.default_float_width = 15
         self.default_int_width = 10
@@ -1868,7 +1871,9 @@ def _decide_how(self):
         if self.vtype in [np.int32, np.float32]:
             self._how = "constant"
         # if a filename was passed in or external path was set
-        elif self._model.external_path is not None or self.vtype == str:
+        elif (
+            self._model is not None and self._model.external_path is not None
+        ) or self.vtype == str:
             if self.format.array_free_format:
                 self._how = "openclose"
             else:
@@ -2710,7 +2715,7 @@ def parse_value(self, value):
             if len(value.shape) == 3 and value.shape[0] == 1:
                 value = value[0]
 
-            if self.model.version == "mfusg":
+            if self.model is not None and self.model.version == "mfusg":
                 if self.shape != value.shape:
                     value = np.array([np.squeeze(value)])