Make the error message more helpful when using non-zero dendritic_delay_fraction with pyNN.brian2 (cf #803)

Author: apdavison

pyNN/brian2/standardmodels/synapses.py

@@ -124,7 +124,8 @@ def __init__(self, timing_dependence=None, weight_dependence=None,
         if dendritic_delay_fraction != 0:
             raise ValueError("The pyNN.brian2 backend does not currently support "
                              "dendritic delays: for the purpose of STDP calculations "
-                             "all delays are assumed to be axonal.")
+                             "all delays are assumed to be axonal. "
+                             "Set dendritic_delay_fraction=0 to avoid this error message.")
         # could perhaps support axonal delays using parrot neurons?
         super(STDPMechanism, self).__init__(timing_dependence, weight_dependence,
                                             voltage_dependence, dendritic_delay_fraction,