pep-484: the pep-484ening, SQL part three

hitting DML which is causing us to open up the
ColumnCollection structure a bit, as we do put anonymous
column expressions with None here.  However, we still want
Table /TableClause to have named column collections that
don't return None, so parametrize the "key" in this
collection also.

* rename some "immutable" elements to "readonly".  we change
  the contents of immutablecolumncollection underneath, so it's
  not "immutable"

Change-Id: I2593995a4e5c6eae874bed5bf76117198be8ae97

1 files changed, 18 insertions, 10 deletions

diff --git a/lib/sqlalchemy/util/_py_collections.py b/lib/sqlalchemy/util/_py_collections.py
index d50352930..1016871aa 100644
--- a/lib/sqlalchemy/util/_py_collections.py
+++ b/lib/sqlalchemy/util/_py_collections.py
@@ -29,37 +29,45 @@ _KT = TypeVar("_KT", bound=Any)
 _VT = TypeVar("_VT", bound=Any)
 
 
-class ImmutableContainer:
+class ReadOnlyContainer:
     __slots__ = ()
 
+    def _readonly(self, *arg: Any, **kw: Any) -> NoReturn:
+        raise TypeError(
+            "%s object is immutable and/or readonly" % self.__class__.__name__
+        )
+
     def _immutable(self, *arg: Any, **kw: Any) -> NoReturn:
         raise TypeError("%s object is immutable" % self.__class__.__name__)
 
     def __delitem__(self, key: Any) -> NoReturn:
-        self._immutable()
+        self._readonly()
 
     def __setitem__(self, key: Any, value: Any) -> NoReturn:
-        self._immutable()
+        self._readonly()
 
     def __setattr__(self, key: str, value: Any) -> NoReturn:
-        self._immutable()
+        self._readonly()
 
 
-class ImmutableDictBase(ImmutableContainer, Dict[_KT, _VT]):
-    def clear(self) -> NoReturn:
+class ImmutableDictBase(ReadOnlyContainer, Dict[_KT, _VT]):
+    def _readonly(self, *arg: Any, **kw: Any) -> NoReturn:
         self._immutable()
 
+    def clear(self) -> NoReturn:
+        self._readonly()
+
     def pop(self, key: Any, default: Optional[Any] = None) -> NoReturn:
-        self._immutable()
+        self._readonly()
 
     def popitem(self) -> NoReturn:
-        self._immutable()
+        self._readonly()
 
     def setdefault(self, key: Any, default: Optional[Any] = None) -> NoReturn:
-        self._immutable()
+        self._readonly()
 
     def update(self, *arg: Any, **kw: Any) -> NoReturn:
-        self._immutable()
+        self._readonly()
 
 
 class immutabledict(ImmutableDictBase[_KT, _VT]):