Handle non-positive dt (#620)

mikeio/dfs/_dfs.py

@@ -147,6 +147,17 @@ def _valid_timesteps(dfsFileInfo: DfsFileInfo, time_steps) -> Tuple[bool, List[i
         TimeAxisType.TimeEquidistant,
     ):
         time_step_file = time_axis.TimeStep
+
+        if time_step_file <= 0:
+
+            if nt > 1:
+                raise ValueError(f"Time step must be a positive number. Time step in the file is {time_step_file} seconds.")
+
+            warnings.warn(
+                f"Time step is {time_step_file} seconds. This must be a positive number. Setting to 1 second."
+            )
+            time_step_file = 1
+
         freq = pd.Timedelta(seconds=time_step_file)
         time = pd.date_range(start_time_file, periods=nt, freq=freq)
     elif time_axis.TimeAxisType == TimeAxisType.CalendarNonEquidistant:

tests/test_dfs2.py

@@ -870,3 +870,17 @@ def test_MIKE_SHE_output():
     assert g2.x[0] == g.x[0] + 30 * g.dx
     assert g2.y[0] == g.y[0] + 35 * g.dy
     assert g2.origin == pytest.approx((g2.x[0], g2.y[0]))
+
+
+def test_read_dfs2_static_dt_zero():
+
+    with pytest.warns(UserWarning, match="positive"):
+        ds = mikeio.read("tests/testdata/single_time_dt_zero.dfs2")
+    assert ds.n_timesteps == 1
+    assert ds.shape == (1, 2, 2)
+
+    with pytest.warns(UserWarning, match="positive"):
+        ds2 = mikeio.read("tests/testdata/single_time_dt_zero.dfs2", time=0)
+
+    assert ds2.shape == (2,2)
+    assert "time" not in ds2.dims