Raise a more specific error (FeatureNotFound) when a requested

  parser or parser feature is not installed. Raise NotImplementedError
  instead of ValueError when the user calls insert_before() or
  insert_after() on the BeautifulSoup object itself. Patch by Aaron
  Devore. [bug=1038301]

3 files changed, 16 insertions, 8 deletions

diff --git a/NEWS.txt b/NEWS.txt
index b7740ce..3557891 100644
--- a/NEWS.txt
+++ b/NEWS.txt
@@ -2,7 +2,11 @@
 
 * Skipped a test under Python 2.6 to avoid a spurious test failure. [bug=1038503]
 
-* 
+* Raise a more specific error (FeatureNotFound) when a requested
+  parser or parser feature is not installed. Raise NotImplementedError
+  instead of ValueError when the user calls insert_before() or
+  insert_after() on the BeautifulSoup object itself. Patch by Aaron
+  Devore. [bug=1038301]
 
 = 4.1.2 (20120817) =
 
diff --git a/bs4/__init__.py b/bs4/__init__.py
index 64f8df9..23afa91 100644
--- a/bs4/__init__.py
+++ b/bs4/__init__.py
@@ -149,7 +149,7 @@ class BeautifulSoup(Tag):
                 features = self.DEFAULT_BUILDER_FEATURES
             builder_class = builder_registry.lookup(*features)
             if builder_class is None:
-                raise ValueError(
+                raise FeatureNotFound(
                     "Couldn't find a tree builder with the features you "
                     "requested: %s. Do you need to install a parser library?"
                     % ",".join(features))
@@ -208,10 +208,10 @@ class BeautifulSoup(Tag):
         return navigable
 
     def insert_before(self, successor):
-        raise ValueError("BeautifulSoup objects don't support insert_before().")
+        raise NotImplementedError("BeautifulSoup objects don't support insert_before().")
 
     def insert_after(self, successor):
-        raise ValueError("BeautifulSoup objects don't support insert_after().")
+        raise NotImplementedError("BeautifulSoup objects don't support insert_after().")
 
     def popTag(self):
         tag = self.tagStack.pop()
@@ -348,6 +348,10 @@ class StopParsing(Exception):
     pass
 
 
+class FeatureNotFound(ValueError):
+    pass
+
+
 #By default, act as an HTML pretty-printer.
 if __name__ == '__main__':
     import sys
diff --git a/bs4/tests/test_tree.py b/bs4/tests/test_tree.py
index 9397f24..5f3395b 100644
--- a/bs4/tests/test_tree.py
+++ b/bs4/tests/test_tree.py
@@ -886,20 +886,20 @@ class TestTreeModification(SoupTest):
         self.assertEqual(
             soup.decode(), self.document_for("QUUX<b>bar</b><a>foo</a>BAZ"))
 
-    def test_insert_after_raises_valueerror_if_after_has_no_meaning(self):
+    def test_insert_after_raises_exception_if_after_has_no_meaning(self):
         soup = self.soup("")
         tag = soup.new_tag("a")
         string = soup.new_string("")
         self.assertRaises(ValueError, string.insert_after, tag)
-        self.assertRaises(ValueError, soup.insert_after, tag)
+        self.assertRaises(NotImplementedError, soup.insert_after, tag)
         self.assertRaises(ValueError, tag.insert_after, tag)
 
-    def test_insert_before_raises_valueerror_if_before_has_no_meaning(self):
+    def test_insert_before_raises_notimplementederror_if_before_has_no_meaning(self):
         soup = self.soup("")
         tag = soup.new_tag("a")
         string = soup.new_string("")
         self.assertRaises(ValueError, string.insert_before, tag)
-        self.assertRaises(ValueError, soup.insert_before, tag)
+        self.assertRaises(NotImplementedError, soup.insert_before, tag)
         self.assertRaises(ValueError, tag.insert_before, tag)
 
     def test_replace_with(self):