Addition of delta keyword argument to unittest.TestCase.assertAlmostEquals and assertNotAlmostEquals

This allows the comparison of objects by specifying a maximum difference; this includes the comparing of non-numeric objects that don't support rounding.

Lib/unittest/case.py

@@ -490,10 +490,12 @@ class TestCase(object):
                                                           safe_repr(second)))
             raise self.failureException(msg)
 
-    def assertAlmostEqual(self, first, second, places=7, msg=None):
+
+    def assertAlmostEqual(self, first, second, places=None, msg=None, delta=None):
         """Fail if the two objects are unequal as determined by their
            difference rounded to the given number of decimal places
-           (default 7) and comparing to zero.
+           (default 7) and comparing to zero, or by comparing that the
+           between the two objects is more than the given delta.
 
            Note that decimal places (from zero) are usually not the same
            as significant digits (measured from the most signficant digit).
@@ -502,29 +504,59 @@ class TestCase(object):
            compare almost equal.
         """
         if first == second:
-            # shortcut for inf
+            # shortcut
             return
-        if round(abs(second-first), places) != 0:
+        if delta is not None and places is not None:
+            raise TypeError("specify delta or places not both")
+
+        if delta is not None:
+            if abs(first - second) <= delta:
+                return
+
+            standardMsg = '%s != %s within %s delta' % (safe_repr(first),
+                                                        safe_repr(second),
+                                                        safe_repr(delta))
+        else:
+            if places is None:
+                places = 7
+
+            if round(abs(second-first), places) == 0:
+                return
+
             standardMsg = '%s != %s within %r places' % (safe_repr(first),
                                                           safe_repr(second),
                                                           places)
         msg = self._formatMessage(msg, standardMsg)
         raise self.failureException(msg)
 
-    def assertNotAlmostEqual(self, first, second, places=7, msg=None):
+    def assertNotAlmostEqual(self, first, second, places=None, msg=None, delta=None):
         """Fail if the two objects are equal as determined by their
            difference rounded to the given number of decimal places
-           (default 7) and comparing to zero.
+           (default 7) and comparing to zero, or by comparing that the
+           between the two objects is less than the given delta.
 
            Note that decimal places (from zero) are usually not the same
            as significant digits (measured from the most signficant digit).
 
            Objects that are equal automatically fail.
         """
-        if (first == second) or round(abs(second-first), places) == 0:
+        if delta is not None and places is not None:
+            raise TypeError("specify delta or places not both")
+        if delta is not None:
+            if not (first == second) and abs(first - second) > delta:
+                return
+            standardMsg = '%s == %s within %s delta' % (safe_repr(first),
+                                                        safe_repr(second),
+                                                        safe_repr(delta))
+        else:
+            if places is None:
+                places = 7
+            if not (first == second) and round(abs(second-first), places) != 0:
+                return
             standardMsg = '%s == %s within %r places' % (safe_repr(first),
                                                          safe_repr(second),
                                                          places)
+
         msg = self._formatMessage(msg, standardMsg)
         raise self.failureException(msg)
 

Lib/unittest/test/test_assertions.py

@@ -1,3 +1,5 @@
+import datetime
+
 import unittest
 
 
@@ -25,6 +27,28 @@ class Test_Assertions(unittest.TestCase):
         self.assertRaises(self.failureException, self.assertNotAlmostEqual,
                           float('inf'), float('inf'))
 
+    def test_AmostEqualWithDelta(self):
+        self.assertAlmostEqual(1.1, 1.0, delta=0.5)
+        self.assertAlmostEqual(1.0, 1.1, delta=0.5)
+        self.assertNotAlmostEqual(1.1, 1.0, delta=0.05)
+        self.assertNotAlmostEqual(1.0, 1.1, delta=0.05)
+
+        self.assertRaises(self.failureException, self.assertAlmostEqual,
+                          1.1, 1.0, delta=0.05)
+        self.assertRaises(self.failureException, self.assertNotAlmostEqual,
+                          1.1, 1.0, delta=0.5)
+
+        self.assertRaises(TypeError, self.assertAlmostEqual,
+                          1.1, 1.0, places=2, delta=2)
+        self.assertRaises(TypeError, self.assertNotAlmostEqual,
+                          1.1, 1.0, places=2, delta=2)
+
+        first = datetime.datetime.now()
+        second = first + datetime.timedelta(seconds=10)
+        self.assertAlmostEqual(first, second,
+                               delta=datetime.timedelta(seconds=20))
+        self.assertNotAlmostEqual(first, second,
+                                  delta=datetime.timedelta(seconds=5))
 
     def test_assertRaises(self):
         def _raise(e):