Use repr() to escape keys in MultiDict __repr__ output

Wrapping keys in literal single quotes produced unparseable output when
keys contained a single quote (e.g. ``"<MultiDict('a'b': 1)>"``). Both
the pure-Python and C-extension code paths now format keys via repr(),
so single quotes and other special characters round-trip correctly.

Author: aiolibsbot

CHANGES/1342.bugfix.rst

@@ -0,0 +1,5 @@
+Fixed ``__repr__`` of :class:`~multidict.MultiDict`,
+:class:`~multidict.CIMultiDict`, their proxies, and the keys/items views
+producing unparseable output when keys contained quote characters --
+keys are now formatted with :func:`repr` so the result is a valid Python
+string literal -- by :user:`aiolibsbot`.

multidict/_multidict_py.py

@@ -103,7 +103,7 @@ def _iter(self, version: int) -> Iterator[tuple[str, _V]]:
     def __repr__(self) -> str:
         lst = []
         for e in self._md._keys.iter_entries():
-            lst.append(f"'{e.key}': {e.value!r}")
+            lst.append(f"{e.key!r}: {e.value!r}")
         body = ", ".join(lst)
         return f"<{self.__class__.__name__}({body})>"
 
@@ -300,7 +300,7 @@ def _iter(self, version: int) -> Iterator[str]:
     def __repr__(self) -> str:
         lst = []
         for e in self._md._keys.iter_entries():
-            lst.append(f"'{e.key}'")
+            lst.append(f"{e.key!r}")
         body = ", ".join(lst)
         return f"<{self.__class__.__name__}({body})>"
 
@@ -753,7 +753,7 @@ def __contains__(self, key: object) -> bool:
 
     @reprlib.recursive_repr()
     def __repr__(self) -> str:
-        body = ", ".join(f"'{e.key}': {e.value!r}" for e in self._keys.iter_entries())
+        body = ", ".join(f"{e.key!r}: {e.value!r}" for e in self._keys.iter_entries())
         return f"<{self.__class__.__name__}({body})>"
 
     if sys.implementation.name != "pypy":
@@ -1207,7 +1207,7 @@ def __contains__(self, key: object) -> bool:
 
     @reprlib.recursive_repr()
     def __repr__(self) -> str:
-        body = ", ".join(f"'{k}': {v!r}" for k, v in self.items())
+        body = ", ".join(f"{k!r}: {v!r}" for k, v in self.items())
         return f"<{self.__class__.__name__}({body})>"
 
     def copy(self) -> MultiDict[_V]:

multidict/_multilib/hashtable.h

@@ -1809,14 +1809,9 @@ md_repr(MultiDictObject *md, PyObject *name, bool show_keys, bool show_values)
             }
         }
         if (show_keys) {
-            if (PyUnicodeWriter_WriteChar(writer, '\'') < 0) {
-                goto fail;
-            }
-            /* Don't need to convert key to istr, the text is the same*/
-            if (PyUnicodeWriter_WriteStr(writer, key) < 0) {
-                goto fail;
-            }
-            if (PyUnicodeWriter_WriteChar(writer, '\'') < 0) {
+            /* Use repr() so keys containing quotes produce parseable output.
+             */
+            if (PyUnicodeWriter_WriteRepr(writer, key) < 0) {
                 goto fail;
             }
         }

tests/test_multidict.py

@@ -635,6 +635,24 @@ def test_repr_aiohttp_issue_410(self, cls: type[MutableMultiMapping[str]]) -> No
 
             assert sys.exc_info()[1] == e  # noqa: PT017
 
+    def test__repr__quotes_keys(self, cls: type[MultiDict[str]]) -> None:
+        # Keys containing quotes must be repr'd as parseable Python literals,
+        # not naively wrapped in single quotes.
+        d = cls([("a'b", "v")])
+        _cls = type(d)
+
+        # repr("a'b") == '"a\'b"' (Python uses double quotes when the string
+        # contains a single quote and no double quote).
+        assert str(d) == f"<{_cls.__name__}(\"a'b\": 'v')>"
+
+    def test_items__repr__quotes_keys(self, cls: type[MultiDict[str]]) -> None:
+        d = cls([("a'b", "v")])
+        assert repr(d.items()) == "<_ItemsView(\"a'b\": 'v')>"
+
+    def test_keys__repr__quotes_keys(self, cls: type[MultiDict[str]]) -> None:
+        d = cls([("a'b", "v")])
+        assert repr(d.keys()) == '<_KeysView("a\'b")>'
+
     @pytest.mark.parametrize(
         "op",
         (operator.or_, operator.and_, operator.sub, operator.xor),