raise an AttributeError when attribute doesn't exists, closes #314

Author: basnijholt

adaptive/learner/integrator_coeffs.py

@@ -186,5 +186,8 @@ def _coefficients():
     return locals()
 
 
-def __getattr__(attr):
-    return _coefficients()[attr]
+def __getattr__(name):
+    try:
+        return _coefficients()[name]
+    except KeyError:
+        raise AttributeError(f"module {__name__} has no attribute {name}")