[FIX] Error message for number of electrodes in implant.stim (#359)

* fix number of electrodes

* fix error message

* add test

pulse2percept/implants/base.py

@@ -164,6 +164,11 @@ def stim(self, data):
                 # Use electrode names as stimulus coordinates:
                 stim = Stimulus(data, electrodes=list(self.earray.keys()))
 
+            if len(stim.electrodes) > self.n_electrodes:
+                raise ValueError("Number of electrodes in the stimulus (%d) "
+                                 "does not match the number of electrodes in "
+                                 "the implant (%d)." % (len(stim.electrodes),
+                                                        self.n_electrodes))
             # Make sure all electrode names are valid:
             for electrode in stim.electrodes:
                 # Invalid index will return None:

pulse2percept/implants/tests/test_base.py

@@ -4,7 +4,7 @@
 import numpy.testing as npt
 from matplotlib.patches import Circle
 
-from pulse2percept.implants import (PointSource, ElectrodeArray,
+from pulse2percept.implants import (PointSource, ElectrodeArray, ElectrodeGrid,
                                     ProsthesisSystem)
 from pulse2percept.stimuli import Stimulus
 
@@ -53,3 +53,10 @@ def test_ProsthesisSystem():
     # Slots:
     npt.assert_equal(hasattr(implant, '__slots__'), True)
     npt.assert_equal(hasattr(implant, '__dict__'), False)
+
+
+def test_ProsthesisSystem_stim():
+    implant = ProsthesisSystem(ElectrodeGrid((13, 13), 20))
+    stim = Stimulus(np.ones((13 * 13 + 1, 5)))
+    with pytest.raises(ValueError):
+        implant.stim = stim