provide Stepsize as float or int

docs/source/userguide/stepsize.rst

@@ -68,4 +68,15 @@ This will modify the stepsize as needed.
         dt_min=1e-6,
         max_stepsize=5,
         milestones=[1, 5, 6, 10]
-        )
+        )
+
+
+.. note::
+
+    When defining the simulation, if your stepsize is constant, you can define it simply by providing it as a `float`` or `int`:
+
+    .. testcode::
+
+        my_model = F.Simulation()
+
+        my_model.dt = 2.0

festim/generic_simulation.py

@@ -182,6 +182,21 @@ def T(self, value):
                 "accepted types for T attribute are int, float, sympy.Expr or festim.Temperature"
             )
 
+    @property
+    def dt(self):
+        return self._dt
+
+    @dt.setter
+    def dt(self, value):
+        if value is None:
+            self._dt = value
+        elif isinstance(value, (int, float)):
+            self._dt = festim.Stepsize(value)
+        elif isinstance(value, festim.Stepsize):
+            self._dt = value
+        else:
+            raise TypeError("dt must be an int, float, or festim.Stepsize")
+
     def attribute_source_terms(self):
         """Assigns the source terms (in self.sources) to the correct field
         (self.mobile, self.T, or traps)

test/unit/test_stepsize.py

@@ -130,3 +130,21 @@ def test_hit_stepsize_max_with_t_stop(time):
     )
     max_stepsize = lambda t: 1 if t >= 1 else None
     assert my_stepsize.adaptive_stepsize["max_stepsize"](time) == max_stepsize(time)
+
+
+@pytest.mark.parametrize("time", [1, 2.5, "coucou", np.array([1, 2]), [1, 2]])
+def test_stepsize_as_value(time):
+    """
+    A test to check that users can pass an int or float to the dt attribute when
+    initialising a F.Simulation class, and an error is raised when passed anything else
+    """
+
+    my_model = festim.Simulation()
+
+    if isinstance(time, (int, float, festim.Stepsize)):
+        my_model.dt = time
+    else:
+        with pytest.raises(
+            TypeError, match="dt must be an int, float, or festim.Stepsize"
+        ):
+            my_model.dt = time