Fix 'Dictionary changed during iteration' exception raising (#628)

* add pypy test

* Lint

* Fix #620: Don't raise 'Dictionary changed during iteration' when the error should not be raised

Co-authored-by: iscai-msft <iscai@microsoft.com>
Co-authored-by: Sam Bull <aa6bs0@sambull.org>

CHANGES/620.bugfix

@@ -0,0 +1 @@
+Fix pure-python implementation that used to raise "Dictionary changed during iteration" error when iterated view (``.keys()``, ``.values()`` or ``.items()``) was created before the dictionary's content change.

multidict/_multidict_py.py

@@ -435,7 +435,6 @@ def __length_hint__(self):
 class _ViewBase:
     def __init__(self, impl):
         self._impl = impl
-        self._version = impl._version
 
     def __len__(self):
         return len(self._impl._items)
@@ -451,11 +450,11 @@ def __contains__(self, item):
         return False
 
     def __iter__(self):
-        return _Iter(len(self), self._iter())
+        return _Iter(len(self), self._iter(self._impl._version))
 
-    def _iter(self):
+    def _iter(self, version):
         for i, k, v in self._impl._items:
-            if self._version != self._impl._version:
+            if version != self._impl._version:
                 raise RuntimeError("Dictionary changed during iteration")
             yield k, v
 
@@ -475,11 +474,11 @@ def __contains__(self, value):
         return False
 
     def __iter__(self):
-        return _Iter(len(self), self._iter())
+        return _Iter(len(self), self._iter(self._impl._version))
 
-    def _iter(self):
+    def _iter(self, version):
         for item in self._impl._items:
-            if self._version != self._impl._version:
+            if version != self._impl._version:
                 raise RuntimeError("Dictionary changed during iteration")
             yield item[2]
 
@@ -499,11 +498,11 @@ def __contains__(self, key):
         return False
 
     def __iter__(self):
-        return _Iter(len(self), self._iter())
+        return _Iter(len(self), self._iter(self._impl._version))
 
-    def _iter(self):
+    def _iter(self, version):
         for item in self._impl._items:
-            if self._version != self._impl._version:
+            if version != self._impl._version:
                 raise RuntimeError("Dictionary changed during iteration")
             yield item[1]
 

tests/test_mutable_multidict.py

@@ -484,3 +484,27 @@ def test_sizeof(self, cls):
     def test_min_sizeof(self, cls):
         md = cls()
         assert sys.getsizeof(md) < 1024
+
+    def test_issue_620_items(self, cls):
+        # https://github.com/aio-libs/multidict/issues/620
+        d = cls({"a": "123, 456", "b": "789"})
+        before_mutation_items = d.items()
+        d["c"] = "000"
+        # This causes an error on pypy.
+        list(before_mutation_items)
+
+    def test_issue_620_keys(self, cls):
+        # https://github.com/aio-libs/multidict/issues/620
+        d = cls({"a": "123, 456", "b": "789"})
+        before_mutation_keys = d.keys()
+        d["c"] = "000"
+        # This causes an error on pypy.
+        list(before_mutation_keys)
+
+    def test_issue_620_values(self, cls):
+        # https://github.com/aio-libs/multidict/issues/620
+        d = cls({"a": "123, 456", "b": "789"})
+        before_mutation_values = d.values()
+        d["c"] = "000"
+        # This causes an error on pypy.
+        list(before_mutation_values)