Resolve "Learner1D fails when function returns a list instead of a numpy.array"

Closes #96 (closed)

adaptive/learner/learner1D.py

@@ -220,7 +220,7 @@ class Learner1D(BaseLearner):
         real = y is not None
         if real:
             # either it is a float/int, if not, try casting to a np.array
-            if type(y) not in [float, int]:
+            if not isinstance(y, (float, int)):
                 y = np.asarray(y, dtype='float64')
 
             # Add point to the real data dict