Update import error messages to suggest installing extras

doc/introduction.rst

@@ -34,6 +34,7 @@ images                      Allows working with image data
 export                      Supports downloading data in a variety of formats (eg TSV, JSON, etc)
 rediscli                    Allows Flask-Admin to display a CLI for Redis
 translation                 Supports translating Flask-Admin into a number of languages
+all                         Installs support for all features
 =========================== ================================================
 
 Once you've chosen the extras you need, install Flask-Admin by specifying them like so::

flask_admin/contrib/appengine/__init__.py

@@ -2,6 +2,9 @@
 try:
     import wtforms_appengine
 except ImportError:
-    raise Exception('Please install wtforms_appengine in order to use appengine backend')
+    raise Exception(
+        'Could not import `wtforms-appengine`. '
+        'Enable `appengine` integration by installing `flask-admin[appengine]`'
+    )
 
 from .view import ModelView

flask_admin/contrib/fileadmin/azure.py

@@ -49,9 +49,11 @@ def __init__(self, container_name, connection_string):
         """
 
         if not BlockBlobService:
-            raise ValueError('Could not import Azure Blob Storage SDK. '
-                             'You can install the SDK using '
-                             'pip install azure-storage-blob')
+            raise ValueError(
+                'Could not import `azure.storage.blob`. '
+                'Enable `azure-blob-storage` integration '
+                'by installing `flask-admin[azure-blob-storage]`'
+            )
 
         self._container_name = container_name
         self._connection_string = connection_string

flask_admin/contrib/fileadmin/s3.py

@@ -56,8 +56,10 @@ def __init__(self, bucket_name, region, aws_access_key_id,
         """
 
         if not s3:
-            raise ValueError('Could not import boto. You can install boto by '
-                             'using pip install boto')
+            raise ValueError(
+                'Could not import `boto`. '
+                'Enable `s3` integration by installing `flask-admin[s3]`'
+            )
 
         connection = s3.connect_to_region(
             region,

flask_admin/contrib/geoa/__init__.py

@@ -3,6 +3,9 @@
     import geoalchemy2
     import shapely
 except ImportError:
-    raise Exception('Please install geoalchemy2 and shapely in order to use geoalchemy integration')
+    raise Exception(
+        'Could not import `geoalchemy2` or `shapely`. '
+        'Enable `geoalchemy` integration by installing `flask-admin[geoalchemy]`'
+    )
 
 from .view import ModelView

flask_admin/contrib/mongoengine/__init__.py

@@ -2,7 +2,10 @@
 try:
     import flask_mongoengine
 except ImportError:
-    raise Exception('Please install flask-mongoengine in order to use mongoengine backend')
+    raise Exception(
+        'Could not import `flask-mongoengine`. '
+        'Enable `mongoengine` integration by installing `flask-admin[mongoengine]`'
+    )
 
 from .view import ModelView
 from .form import EmbeddedForm

flask_admin/contrib/peewee/__init__.py

@@ -3,6 +3,9 @@
     import peewee
     import wtfpeewee
 except ImportError:
-    raise Exception('Please install peewee and wtf-peewee packages in order to use peewee integration')
+    raise Exception(
+        'Could not import `peewee` or `wtfpeewee`. '
+        'Enable `peewee` integration by installing `flask-admin[peewee]`'
+    )
 
 from .view import ModelView

flask_admin/contrib/pymongo/__init__.py

@@ -2,6 +2,9 @@
 try:
     import pymongo
 except ImportError:
-    raise Exception('Please install pymongo in order to use pymongo integration')
+    raise Exception(
+        'Could not import `pymongo`. '
+        'Enable `pymongo` integration by installing `flask-admin[pymongo]`'
+    )
 
 from .view import ModelView

flask_admin/form/upload.py

@@ -387,7 +387,10 @@ class MyForm(BaseForm):
         """
         # Check if PIL is installed
         if Image is None:
-            raise ImportError('PIL library was not found')
+            raise Exception(
+                'Could not import `PIL`. '
+                'Enable `images` integration by installing `flask-admin[images]`'
+            )
 
         self.max_size = max_size
         self.thumbnail_fn = thumbgen or thumbgen_filename

flask_admin/model/base.py

@@ -2356,8 +2356,10 @@ def _export_tablib(self, export_type, return_url):
             Exports a variety of formats using the tablib library.
         """
         if tablib is None:
-            flash(gettext('Tablib dependency not installed.'), 'error')
-            return redirect(return_url)
+            raise Exception(
+                'Could not import `tablib`. '
+                'Enable `export` integration by installing `flask-admin[export]`'
+            )
 
         filename = self.get_export_name(export_type)