Show a more helpful error message when a restart is required for %view

extensions/positron-python/python_files/positron/positron_ipykernel/data_explorer.py

@@ -23,6 +23,7 @@
 )
 
 import comm
+from IPython.core.error import UsageError
 
 from .access_keys import decode_access_key
 from .data_explorer_comm import (
@@ -96,7 +97,14 @@
     TextSearchType,
 )
 from .positron_comm import CommMessage, PositronComm
-from .third_party import np_, pd_, pl_
+from .third_party import (
+    RestartRequiredError,
+    import_pandas,
+    import_polars,
+    np_,
+    pd_,
+    pl_,
+)
 from .utils import BackgroundJobQueue, guid
 
 if TYPE_CHECKING:
@@ -312,6 +320,7 @@ def _match_text_search(params: FilterTextSearch):
 
                 def matches(x):
                     return term in x.lower()
+
             else:
 
                 def matches(x):
@@ -2581,11 +2590,31 @@ class PyArrowView(DataExplorerTableView):
 
 
 def _is_pandas(table):
-    return pd_ is not None and isinstance(table, (pd_.DataFrame, pd_.Series))
+    pandas = import_pandas()
+    if pandas is not None and isinstance(table, (pandas.DataFrame, pandas.Series)):
+        # If pandas was installed after the kernel was started, pd_ will still be None.
+        # Raise an error to inform the user to restart the kernel.
+        if pd_ is None:
+            raise RestartRequiredError(
+                "Pandas was installed after the session started. Please restart the session to "
+                + "view the table in the Data Explorer."
+            )
+        return True
+    return False
 
 
 def _is_polars(table):
-    return pl_ is not None and isinstance(table, (pl_.DataFrame, pl_.Series))
+    polars = import_polars()
+    if polars is not None and isinstance(table, (polars.DataFrame, polars.Series)):
+        # If polars was installed after the kernel was started, pl_ will still be None.
+        # Raise an error to inform the user to restart the kernel.
+        if pl_ is None:
+            raise RestartRequiredError(
+                "Polars was installed after the session started. Please restart the session to "
+                + "view the table."
+            )
+        return True
+    return False
 
 
 def _get_table_view(

extensions/positron-python/python_files/positron/positron_ipykernel/positron_ipkernel.py

@@ -37,6 +37,7 @@
 from .patch.holoviews import set_holoviews_extension
 from .plots import PlotsService
 from .session_mode import SessionMode
+from .third_party import RestartRequiredError
 from .ui import UiService
 from .utils import BackgroundJobQueue, JsonRecord, get_qualname
 from .variables import VariablesService
@@ -168,6 +169,8 @@ def view(self, line: str) -> None:
             )
         except TypeError:
             raise UsageError(f"cannot view object of type '{get_qualname(obj)}'")
+        except RestartRequiredError as error:
+            raise UsageError(*error.args)
 
     @magic_arguments.magic_arguments()
     @magic_arguments.argument(

extensions/positron-python/python_files/positron/positron_ipykernel/tests/test_data_explorer.py

@@ -11,14 +11,15 @@
 from datetime import datetime
 from decimal import Decimal
 from io import StringIO
-from typing import Any, Dict, List, Optional, Type, cast
+from typing import Any, Dict, List, Optional, Type, Union, cast
 
 import numpy as np
 import pandas as pd
 import polars as pl
 import pytest
 import pytz
 
+from .. import data_explorer
 from .._vendor.pydantic import BaseModel
 from ..access_keys import encode_access_key
 from ..data_explorer import (
@@ -49,6 +50,7 @@
     RowFilterTypeSupportStatus,
     SupportStatus,
 )
+from ..third_party import RestartRequiredError
 from ..utils import guid
 from .conftest import DummyComm, PositronShell
 from .test_variables import BIG_ARRAY_LENGTH
@@ -295,6 +297,30 @@ def test_register_table_with_variable_path(de_service: DataExplorerService):
     assert table_view.state.name == title
 
 
+@pytest.mark.parametrize(
+    ("table", "import_name", "title"),
+    [(pd.DataFrame({}), "pd_", "Pandas"), (pl.DataFrame({}), "pl_", "Polars")],
+)
+def test_register_table_after_installing_dependency(
+    table: Union[pd.DataFrame, pl.DataFrame],
+    import_name: str,
+    title: str,
+    de_service: DataExplorerService,
+    monkeypatch,
+):
+    # Patch the module (e.g. third_party.pd_) to None. Since these packages are really is installed
+    # during tests, this simulates the case where the user installs the package after the kernel
+    # starts, therefore the third_party attribute (e.g. pd_) is None but the corresponding import
+    # function (third_party.import_pandas()) returns the module.
+    # See https://github.com/posit-dev/positron/issues/5535.
+    monkeypatch.setattr(data_explorer, import_name, None)
+
+    with pytest.raises(
+        RestartRequiredError, match=f"^{title} was installed after the session started."
+    ):
+        de_service.register_table(table, "test_table")
+
+
 def test_shutdown(de_service: DataExplorerService):
     df = pd.DataFrame({"a": [1, 2, 3, 4, 5]})
     de_service.register_table(df, "t1", comm_id=guid())

extensions/positron-python/python_files/positron/positron_ipykernel/third_party.py

@@ -9,47 +9,53 @@
 # checking.
 
 
-def _get_numpy():
+class RestartRequiredError(Exception):
+    """Raised when a restart is required to load a third party package."""
+
+    pass
+
+
+def import_numpy():
     try:
         import numpy
     except ImportError:
         numpy = None
     return numpy
 
 
-def _get_pandas():
+def import_pandas():
     try:
         import pandas
     except ImportError:
         pandas = None
     return pandas
 
 
-def _get_polars():
+def import_polars():
     try:
         import polars
     except ImportError:
         polars = None
     return polars
 
 
-def _get_torch():
+def import_torch():
     try:
         import torch  # type: ignore [reportMissingImports] for 3.12
     except ImportError:
         torch = None
     return torch
 
 
-def _get_pyarrow():
+def import_pyarrow():
     try:
         import pyarrow  # type: ignore [reportMissingImports] for 3.12
     except ImportError:
         pyarrow = None
     return pyarrow
 
 
-def _get_sqlalchemy():
+def import_sqlalchemy():
     try:
         import sqlalchemy
     except ImportError:
@@ -59,11 +65,12 @@ def _get_sqlalchemy():
 
 # Currently, pyright only correctly infers the types below as `Optional` if we set their values
 # using function calls.
-np_ = _get_numpy()
-pa_ = _get_pyarrow()
-pd_ = _get_pandas()
-pl_ = _get_polars()
-torch_ = _get_torch()
-sqlalchemy_ = _get_sqlalchemy()
+np_ = import_numpy()
+pa_ = import_pyarrow()
+pd_ = import_pandas()
+pl_ = import_polars()
+torch_ = import_torch()
+sqlalchemy_ = import_sqlalchemy()
+
 
 __all__ = ["np_", "pa_", "pd_", "pl_", "torch_", "sqlalchemy_"]