Undefined name 'value'... Change to 'values' * 3

The function parameter in __reducer(self, key, value):__ is __value__ (without an _s_) but the function body uses __values__ with an _s_ which creates an undefined name.  Solution: change the function parameter from __value__ to __values__.

solutions/system_design/mint/mint_mapreduce.py

@@ -35,7 +35,7 @@ class SpendingByCategory(MRJob):
         if period == self.current_year_month():
             yield (period, category), amount
 
-    def reducer(self, key, value):
+    def reducer(self, key, values):
         """Sum values for each key.
 
         (2016-01, shopping), 125