force user_ns to be a dict, as we call .clear() on it in IPython

Author: Carreau

ipykernel/embed.py

@@ -52,6 +52,7 @@ def embed_kernel(module=None, local_ns=None, **kwargs):
         local_ns = caller_locals
 
     app.kernel.user_module = module
+    assert isinstance(local_ns, dict)
     app.kernel.user_ns = local_ns
     app.shell.set_completer_frame()  # type:ignore[union-attr]
     app.start()

ipykernel/ipkernel.py

@@ -18,7 +18,18 @@
 from IPython.core import release
 from IPython.utils.tokenutil import line_at_cursor, token_at_cursor
 from jupyter_client.session import extract_header
-from traitlets import Any, Bool, HasTraits, Instance, List, Type, default, observe, observe_compat
+from traitlets import (
+    Any,
+    Bool,
+    Dict,
+    HasTraits,
+    Instance,
+    List,
+    Type,
+    default,
+    observe,
+    observe_compat,
+)
 
 from .comm.comm import BaseComm
 from .comm.manager import CommManager
@@ -86,7 +97,7 @@ def _user_module_changed(self, change):
         if self.shell is not None:
             self.shell.user_module = change["new"]
 
-    user_ns = Instance("collections.abc.Mapping", allow_none=True)
+    user_ns = Dict(allow_none=True)
 
     @default("user_ns")
     def _default_user_ns(self):