Avoid over-eager KeyError on empty dict.pop

crosshair/simplestructs.py

@@ -243,17 +243,18 @@ def _lastitem(self):
     def pop(self, key, default=_MISSING):
         # CPython checks the empty case before attempting to hash the key.
         # So this must happen before the hash-ability check:
-        if self._len == 0:
-            raise KeyError
-        try:
-            value = self[key]
-        except KeyError:
-            if default is _MISSING:
-                raise
-            return default
-        else:
-            del self[key]
-            return value
+        if self._len > 0:
+            try:
+                value = self[key]
+            except KeyError:
+                pass
+            else:
+                del self[key]
+                return value
+        # Not found:
+        if default is _MISSING:
+            raise
+        return default
 
     def popitem(self):
         for key in self._reversed():

crosshair/simplestructs_test.py

@@ -37,6 +37,13 @@ def test_ShellMutableMap_popitem_ordering() -> None:
     assert SimpleDict([("c", "d"), ("a", "b")]).popitem() == ("a", "b")
 
 
+def test_ShellMutableMap_pop_with_default() -> None:
+    assert {"c": "d", "a": "b"}.popitem() == ("a", "b")
+    assert ShellMutableMap({}).pop("a", "x") == "x"
+    assert ShellMutableMap({"a": "b"}).pop("a", "x") == "b"
+    assert ShellMutableMap({"a": "b"}).pop("c", "x") == "x"
+
+
 def test_ShellMutableMap_poo() -> None:
     m = ShellMutableMap({2: 0})
     assert 0 == m.setdefault(2.0, {True: "0"})