move some imports into TYPE_CHECKING

Author: dantownsend

piccolo/query/methods/alter.py

@@ -3,14 +3,15 @@
 import itertools
 import typing as t
 
-from piccolo.columns.base import Column, OnDelete, OnUpdate
+from piccolo.columns.base import Column
 from piccolo.columns.column_types import ForeignKey, Varchar, Numeric
 from piccolo.query.base import Query
 from piccolo.querystring import QueryString
 from piccolo.utils.warnings import colored_warning, Level
 
 if t.TYPE_CHECKING:  # pragma: no cover
     from piccolo.table import Table
+    from piccolo.columns.base import OnDelete, OnUpdate
 
 
 @dataclass

piccolo/table.py

@@ -6,7 +6,7 @@
 import typing as t
 
 from piccolo.engine import Engine, engine_finder
-from piccolo.columns import Column, Selectable
+from piccolo.columns import Column
 from piccolo.columns.column_types import (
     ForeignKey,
     JSON,
@@ -41,6 +41,9 @@
 from piccolo.querystring import QueryString, Unquoted
 from piccolo.utils import _camel_to_snake
 
+if t.TYPE_CHECKING:
+    from piccolo.columns import Selectable
+
 
 PROTECTED_TABLENAMES = ("user",)