Initial ORM typing layout

introduces:

1. new mapped_column() helper
2. DeclarativeBase helper
3. declared_attr has been re-typed
4. rework of Mapped[] to return InstrumentedAtribute for
   class get, so works without Mapped itself having expression
   methods
5. ORM constructs now generic on [_T]

also includes some early typing work, most of which will
be in later commits:

1. URL and History become typing.NamedTuple
2. come up with type-checking friendly way of type
   checking cy extensions, where type checking will be applied
   to the py versions, just needed to come up with a succinct
   conditional pattern for the imports

References: #6810
References: #7535
References: #7562
Change-Id: Ie5d9a44631626c021d130ca4ce395aba623c71fb

1 files changed, 6 insertions, 1 deletions

diff --git a/lib/sqlalchemy/sql/functions.py b/lib/sqlalchemy/sql/functions.py
index 7a1e80889..2e6d64c55 100644
--- a/lib/sqlalchemy/sql/functions.py
+++ b/lib/sqlalchemy/sql/functions.py
@@ -9,6 +9,9 @@
 
 """
 
+from typing import Any
+from typing import TypeVar
+
 from . import annotation
 from . import coercions
 from . import operators
@@ -42,6 +45,8 @@ from .visitors import InternalTraversal
 from .. import util
 
 
+_T = TypeVar("_T", bound=Any)
+
 _registry = util.defaultdict(dict)
 
 
@@ -67,7 +72,7 @@ def register_function(identifier, fn, package="_default"):
     reg[identifier] = fn
 
 
-class FunctionElement(Executable, ColumnElement, FromClause, Generative):
+class FunctionElement(Executable, ColumnElement[_T], FromClause, Generative):
     """Base for SQL function-oriented constructs.
 
     .. seealso::