add delta argument to assert_almost_equal

Fixes #1

Author: srittau

asserts.py

@@ -72,11 +72,21 @@ def assert_not_equal(first, second, msg=None):
         fail(msg or "{!r} == {!r}".format(first, second))
 
 
-def assert_almost_equal(first, second, places=7, msg=None):
+def assert_almost_equal(first, second, places=None, msg=None, delta=None):
     """Fail if the two objects are unequal when rounded."""
-    if round(second - first, places):
-        fail(msg or "{!r} != {!r} within {} places".format(first, second,
-                                                           places))
+    if delta is not None and places is not None:
+        raise TypeError("'places' and 'delta' are mutually exclusive")
+    if delta is not None:
+        diff = second - first
+        success = diff < delta
+        detail_msg = "with delta={}".format(delta)
+    else:
+        if places is None:
+            places = 7
+        success = not round(second - first, places)
+        detail_msg = "within {} places".format(places)
+    if not success:
+        fail(msg or "{!r} != {!r} ".format(first, second) + detail_msg)
 
 
 def assert_regex(text, regex, msg=None):

test_asserts.py

@@ -180,13 +180,27 @@ def test_assert_not_equal__equal__custom_message(self):
     def test_assert_almost_equal__same(self):
         assert_almost_equal(5, 5)
 
-    def test_assert_almost_equal__similar(self):
+    def test_assert_almost_equal__similar__defaults(self):
+        assert_almost_equal(5, 5.00000001)
+
+    def test_assert_almost_equal__similar__places(self):
         assert_almost_equal(5, 5.0001, places=3)
 
+    def test_assert_almost_equal__similar__delta(self):
+        assert_almost_equal(5, 5.001, delta=0.1)
+
     def test_assert_almost_equal__not_similar__default_message(self):
         with _assert_raises_assertion("5 != 5.0001 within 7 places"):
             assert_almost_equal(5, 5.0001)
 
+    def test_assert_almost_equal__not_similar__places__default_message(self):
+        with _assert_raises_assertion("5 != 6 within 3 places"):
+            assert_almost_equal(5, 6, places=3)
+
+    def test_assert_almost_equal__not_similar__delta__default_message(self):
+        with _assert_raises_assertion("5 != 6 with delta=0.1"):
+            assert_almost_equal(5, 6, delta=0.1)
+
     def test_assert_almost_equal__not_similar__custom_message(self):
         with _assert_raises_assertion("test message"):
             assert_almost_equal(5, -5, msg="test message")
@@ -199,6 +213,14 @@ def test_assert_almost_equal__wrong_types(self):
         else:
             raise AssertionError("TypeError not raised")
 
+    def test_assert_almost_equal__places_and_delta(self):
+        try:
+            assert_almost_equal(5, 5, places=3, delta=0.0003)
+        except TypeError:
+            pass
+        else:
+            raise AssertionError("TypeError not raised")
+
     def test_assert_regex__matches_string(self):
         assert_regex("This is a test text", "is.*test")