BUG: fix brentq doesn't raise error in singlediode (pvlib#556)

mikofski · wholmgren · commit affc1bf19743 · 2018-09-04T16:04:09.000-07:00
* if `brentq` is called in `singlediode.py` but no SciPy, then should raise an exception
* currently using `NotImplemented` raises TypeError: 'NotImplementedType' object is not callable because `NotImplemented` is a constant
diff --git a/pvlib/singlediode.py b/pvlib/singlediode.py
@@ -13,7 +13,8 @@
 try:
     from scipy.optimize import brentq
 except ImportError:
-    brentq = NotImplemented
+    def brentq(): raise NotImplementedError(
+        "brentq can't be imported because scipy isn't installed")
 
 # FIXME: change this to newton when scipy-1.2 is released
 try:
