CountVector: Add abs

This is generally useful and will help me evolving the clone detection
routines further.

bears/codeclone_detection/CountVector.py

@@ -1,3 +1,6 @@
+from math import sqrt
+
+
 class CountVector:
     def __init__(self, name, conditions=None, weightings=None):
         """
@@ -52,6 +55,9 @@ def __len__(self):
     def __iter__(self):
         return iter(self.count_vector)
 
+    def __abs__(self):
+        return sqrt(sum(x**2 for x in self))
+
     def difference(self, other):
         """
         Calculates a normalized difference. This value can be used to indicate

bears/tests/codeclone_detection/CountVectorTest.py

@@ -1,3 +1,4 @@
+from math import sqrt
 import sys
 
 sys.path.insert(0, ".")
@@ -62,6 +63,15 @@ def test_cloning(self):
         self.assertEqual(clone.conditions, uut.conditions)
         self.assertEqual(clone.count_vector, [0])
 
+    def test_abs(self):
+        uut = CountVector("varname",
+                          [lambda x: True, lambda x: x])
+        self.assertEqual(abs(uut), 0)
+        uut.count_reference(True)
+        self.assertEqual(abs(uut), sqrt(2))
+        uut.count_reference(False)
+        self.assertEqual(abs(uut), sqrt(5))
+
     def check_difference(self, cv1, cv2, expected_difference):
         """
         Checks the difference between the given count vectors.