Added subscript operator with precedence equal to power.

line.py

@@ -4,7 +4,7 @@ from traverse import traverse_depth_first
 OPERATORS = [
         ('+', '-'),
         ('*', '/', 'mod'),
-        ('^', )
+        ('^', '_')
         ]
 
 MAX_PRED = len(OPERATORS)

tests/test_line.py

@@ -38,6 +38,9 @@ class TestLine(unittest.TestCase):
         power = N('^', l0, N('^', N('^', l1, l2), l3))
         self.assertEquals(generate_line(power), '1 ^ (2 ^ 3) ^ 4')
 
+        power = N('^', l0, N('^', N('_', l1, l2), l3))
+        self.assertEquals(generate_line(power), '1 ^ (2 _ 3) ^ 4')
+
     def test_parentheses_equal_precedence_left(self):
         a, b, c, d = L('a'), L('b'), L('c'), L('d')
         exp = N('*', N('/', N('*', a, b), c), d)