I think I prefer this more explicit implementation of assertInterpolationEqual()

Author: davepeck

Lib/test/test_string/_support.py

@@ -11,23 +11,30 @@ def assertInterpolationEqual(self, i, exp):
         (value, expression, conversion, format_spec) where the final three
         items may be omitted and are assumed to be '', None and '' respectively.
         """
-        # Merge in defaults for expression, conversion, and format_spec
-        defaults = ('', None, '')
-        expected = exp + defaults[len(exp) - 1:]
-
-        actual = (i.value, i.expression, i.conversion, i.format_spec)
-        self.assertEqual(actual, expected)
-
+        if len(exp) == 4:
+            actual = (i.value, i.expression, i.conversion, i.format_spec)
+            self.assertEqual(actual, exp)
+        elif len(exp) == 3:
+            self.assertEqual((i.value, i.expression, i.conversion), exp)
+            self.assertEqual(i.format_spec, "")
+        elif len(exp) == 2:
+            self.assertEqual((i.value, i.expression), exp)
+            self.assertEqual(i.conversion, None)
+            self.assertEqual(i.format_spec, "")
+        elif len(exp) == 1:
+            self.assertEqual((i.value,), exp)
+            self.assertEqual(i.expression, "")
+            self.assertEqual(i.conversion, None)
+            self.assertEqual(i.format_spec, "")
 
     def assertTStringEqual(self, t, strings, interpolations):
         """Test template string literal equality.
 
         The *strings* argument must be a tuple of strings equal to *t.strings*.
 
         The *interpolations* argument must be a sequence of tuples which are
-        compared against *t.interpolations*. Each tuple consists of
-        (value, expression, conversion, format_spec), though the final three
-        items may be omitted and are assumed to be '' None, and '' respectively.
+        compared against *t.interpolations*. Each tuple must match the form
+        described in the `assertInterpolationEqual` method.
         """
         self.assertEqual(t.strings, strings)
         self.assertEqual(len(t.interpolations), len(interpolations))