Issue alert if calc wake needs to be run

examples/make_error.py

@@ -0,0 +1,15 @@
+
+
+from floris.tools import FlorisInterface
+
+
+fi = FlorisInterface("inputs/gch.yaml")
+
+# # Convert to a simple two turbine layout
+# fi.reinitialize( layout=( [0, 500.], [0., 0.] ) )
+
+
+# fi.calculate_wake()
+
+# Get the turbine powers
+turbine_powers = fi.get_turbine_powers()/1000.

floris/tools/floris_interface.py

@@ -558,12 +558,20 @@ def check_wind_condition_for_viz(self, wd=None, ws=None):
         if len(ws) > 1 or len(ws) < 1:
             raise ValueError("Wind speed input must be of length 1 for visualization. Current length is {}.".format(len(ws)))
 
+    def check_calc_wake_run(self, func_name):
+
+        if not hasattr('self.floris.farm', 'turbine_type_map'):
+            raise AttributeError('Cant call function %s without first calling calculate_wake' % func_name)
+
     def get_turbine_powers(self) -> NDArrayFloat:
         """Calculates the power at each turbine in the windfarm.
 
         Returns:
             NDArrayFloat: [description]
         """
+
+        self.check_calc_wake_run('get_turbine_powers')
+
         turbine_powers = power(
             air_density=self.floris.flow_field.air_density,
             velocities=self.floris.flow_field.u,