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, 4 insertions, 1 deletions

diff --git a/lib/sqlalchemy/sql/util.py b/lib/sqlalchemy/sql/util.py
index 5114a2431..cdce49f7b 100644
--- a/lib/sqlalchemy/sql/util.py
+++ b/lib/sqlalchemy/sql/util.py
@@ -15,6 +15,7 @@ from itertools import chain
 import typing
 from typing import Any
 from typing import cast
+from typing import Iterator
 from typing import Optional
 
 from . import coercions
@@ -33,6 +34,7 @@ from .elements import _find_columns  # noqa
 from .elements import _label_reference
 from .elements import _textual_label_reference
 from .elements import BindParameter
+from .elements import ClauseElement  # noqa
 from .elements import ColumnClause
 from .elements import ColumnElement
 from .elements import Grouping
@@ -51,6 +53,7 @@ from .. import exc
 from .. import util
 
 if typing.TYPE_CHECKING:
+    from .roles import FromClauseRole
     from ..engine.interfaces import _AnyExecuteParams
     from ..engine.interfaces import _AnyMultiExecuteParams
     from ..engine.interfaces import _AnySingleExecuteParams
@@ -404,7 +407,7 @@ def clause_is_present(clause, search):
         return False
 
 
-def tables_from_leftmost(clause):
+def tables_from_leftmost(clause: FromClauseRole) -> Iterator[FromClause]:
     if isinstance(clause, Join):
         for t in tables_from_leftmost(clause.left):
             yield t