Improve the logic behind importing a module

docs/how_to/validate.md

@@ -8,25 +8,25 @@ This guide shows you how to validate the `YAML file` that specifies a Lumen dash
 ## Run the specification routine
 Use the `lumen validate` command line tool to run the validation. Insert the path to your specification file in place of `<dashboard.yml>` below.
 
-```console
+```bash
 lumen validate <dashboard.yaml>
 ```
 
 ## Debug an invalid specification file
 When the validation fails, it will provide an error message indicating the type and location of the issue.
 
-### Indendation errors
-Indendation errors often show up as "`expected... but found...`"
+### Indentation errors
+Indentation errors often show up as "`expected... but found...`"
 
-```console
+```python-traceback
 expected <block end>, but found '?'
   in "<unicode string>", line 28, column 3:
       facet:
       ^
 ```
 
 They may also appear as messages about certain values not being allowed in this hierarchy level:
-```console
+```python-traceback
 ERROR: mapping values are not allowed here
   in "<unicode string>", line 6, column 11:
         shared: true
@@ -37,7 +37,7 @@ ERROR: mapping values are not allowed here
 
 For constrained key and value fields, invalid entries will get caught, and a recommendation may be provided:
 
-```console
+```python-traceback
 View component specification declared unknown type 'hvplotqedq'. Did you mean 'hvplot or 'hvplot_ui'?
 
     table: southern_rockies
@@ -55,12 +55,13 @@ View component specification declared unknown type 'hvplotqedq'. Did you mean 'h
 ### Package not installed
 The validation will also catch the declaration of packages not installed. For example:
 
-```console
-Source component specification declared unknown type 'intake'.
+```bash
+ERROR: In order to use the source component 'intake', the 'intake' package must be installed. It can be installed with:
+  conda install intake
 ```
 
-In this case, simply install the package into your enviornment, such as with:
+In this case, simply follow the instruction and install the package into your environment, such as with:
 
-```console
+```bash
 conda install intake
 ```

lumen/base.py

@@ -363,10 +363,19 @@ def _get_type(cls, component_type, spec=None):
             )
         if '.' in component_type:
             return resolve_module_reference(component_type, base_type)
+
         try:
-            __import__(f'lumen.{base_type.__name__.lower()}s.{component_type}')
-        except Exception:
-            pass
+            import_name = f'lumen.{base_type.__name__.lower()}s.{component_type}'
+            __import__(import_name)
+        except ImportError as e:
+            if e.name != import_name:
+                msg = (
+                    f"In order to use the {base_type.__name__.lower()} "
+                    f"component '{component_type}', the '{e.name}' package "
+                    "must be installed. It can be installed with:"
+                    f"\n  conda install {e.name}"
+                )
+                raise ImportError(msg)
 
         subcls_types = set()
         for subcls in param.concrete_descendents(cls).values():