only call the callback when we would output data

src/acom_music_box/music_box.py

@@ -539,6 +539,11 @@ def solve(self, output_path=None, callback=None):
                 output_array.append(row)
                 next_output_time += self.box_model_options.output_step_time
 
+                # calls callback function if present
+                if callback is not None:
+                    df = pd.DataFrame(output_array[:-1], columns=output_array[0])
+                    callback(df, curr_time, curr_conditions, self.box_model_options.simulation_length)
+
             # ensure the time step is not greater than the next update to the
             # evolving conditions or the next output time
             time_step = self.box_model_options.chem_step_time
@@ -561,12 +566,6 @@ def solve(self, output_path=None, callback=None):
 
             # increments time
             curr_time += time_step
-
-            # calls callback function if present
-            if callback is not None:
-                df = pd.DataFrame(output_array[:-1], columns=output_array[0])
-                callback(df, curr_time, curr_conditions, self.box_model_options.simulation_length)
-
         df = pd.DataFrame(output_array[1:], columns=output_array[0])
         # outputs to file if output is present
         if output_path is not None: