Add typing for shell attribute of SpyderPdb

Also, fix imports ordering and code style in the module that contains
that class.

Author: ccordoba12

spyder_kernels/customize/spyderpdb.py

@@ -7,17 +7,20 @@
 
 """Spyder debugger."""
 
+from __future__ import annotations
+
 import ast
 import bdb
 import builtins
 from contextlib import contextmanager
+from collections import namedtuple
+from functools import lru_cache
 import logging
 import os
 import sys
 import traceback
 import threading
-from collections import namedtuple
-from functools import lru_cache
+import typing
 
 from IPython.core.autocall import ZMQExitAutocall
 from IPython.core.debugger import Pdb as ipyPdb
@@ -27,10 +30,16 @@
 from spyder_kernels.comms.commbase import stacksummary_to_json
 from spyder_kernels.comms.frontendcomm import CommError, frontend_request
 from spyder_kernels.customize.utils import (
-    path_is_library, capture_last_Expr, exec_encapsulate_locals
+    path_is_library,
+    capture_last_Expr,
+    exec_encapsulate_locals,
 )
 
 
+if typing.TYPE_CHECKING:
+    from spyder_kernels.console.shell import SpyderShell
+
+
 logger = logging.getLogger(__name__)
 
 
@@ -85,7 +94,9 @@ def __init__(self, completekey='tab', stdin=None, stdout=None,
         self._exclamation_warning_printed = False
         self.pdb_stop_first_line = True
         self._disable_next_stack_entry = False
-        super(SpyderPdb, self).__init__()
+        self.shell: SpyderShell | None = None
+
+        super().__init__()
 
         # content of tuple: (filename, line number)
         self._previous_step = None