Backport PR #23377 on branch 6.x (PR: Improve message when a variable…

… can't be viewed due to a missing module (Variable Explorer)) (#23584)

spyder/plugins/ipythonconsole/widgets/namespacebrowser.py

@@ -19,7 +19,7 @@
 from spyder_kernels.comms.commbase import CommError
 
 # Local imports
-from spyder.config.base import _
+from spyder.config.base import _, is_conda_based_app
 
 # For logging
 logger = logging.getLogger(__name__)
@@ -42,6 +42,16 @@ def get_value(self, name):
         reason_other = _("An unkown error occurred. Check the console because "
                          "its contents could have been printed there")
         reason_comm = _("The comm channel is not working")
+        reason_missing_package_installer = _(
+            "The '{}' package is required to open this variable. "
+            "Unfortunately, it's not part of our installer, which means your "
+            "variable can't be displayed by Spyder."
+        )
+        reason_missing_package = _(
+            "The '{}' package is required to open this variable and it's not "
+            "installed alongside Spyder. To fix this problem, please install "
+            "it in the same environment that you use to run Spyder."
+        )
         msg = _("<br><i>%s.</i><br><br><br>"
                 "<b>Note</b>: Please don't report this problem on Github, "
                 "there's nothing to do about it.")
@@ -63,6 +73,15 @@ def get_value(self, name):
             raise
         except CommError:
             raise ValueError(msg % reason_comm)
+        except ModuleNotFoundError as e:
+            if is_conda_based_app():
+                raise ValueError(
+                    msg % reason_missing_package_installer.format(e.name)
+                )
+            else:
+                raise ValueError(
+                    msg % reason_missing_package.format(e.name)
+                )
         except Exception:
             raise ValueError(msg % reason_other)