Fix bug when setting existing key in full dict

Minimal version of PR mailgun#32 without adding a counter.

expiringdict/__init__.py

@@ -89,10 +89,13 @@ def __setitem__(self, key, value, set_time=None):
         """ Set d[key] to value. """
         with self.lock:
             if len(self) == self.max_len:
-                try:
-                    self.popitem(last=False)
-                except KeyError:
-                    pass
+                if key in self:
+                    del self[key]
+                else:
+                    try:
+                        self.popitem(last=False)
+                    except KeyError:
+                        pass
             if set_time is None:
                 set_time = time.time()
             OrderedDict.__setitem__(self, key, (value, set_time))

tests/expiringdict_test.py

@@ -122,3 +122,14 @@ def test_not_implemented():
     assert_raises(NotImplementedError, d.viewitems)
     assert_raises(NotImplementedError, d.viewkeys)
     assert_raises(NotImplementedError, d.viewvalues)
+
+
+def test_reset_of_key_no_trim():
+    """Re-setting an existing key should not cause a non-expired key to be dropped"""
+    d = ExpiringDict(max_len=2, max_age_seconds=10)
+    d["a"] = "A"
+    d["b"] = "B"
+
+    d["b"] = "B"
+
+    assert "a" in d