Improved the exception raised when you call .unwrap() or

  .replace_with() on an element that's not attached to a tree.

3 files changed, 22 insertions, 1 deletions

diff --git a/NEWS.txt b/NEWS.txt
index 768b96f..6ba5275 100644
--- a/NEWS.txt
+++ b/NEWS.txt
@@ -58,6 +58,9 @@
 * Fixed a crash in Unicode, Dammit's encoding detector when the name
   of the encoding itself contained invalid bytes. [bug=1360913]
 
+* Improved the exception raised when you call .unwrap() or
+  .replace_with() on an element that's not attached to a tree.
+
 = 4.3.2 (20131002) =
 
 * Fixed a bug in which short Unicode input was improperly encoded to
diff --git a/bs4/element.py b/bs4/element.py
index 3c32c17..2ea68b3 100644
--- a/bs4/element.py
+++ b/bs4/element.py
@@ -215,6 +215,10 @@ class PageElement(object):
     previousSibling = _alias("previous_sibling")  # BS3
 
     def replace_with(self, replace_with):
+        if not self.parent:
+            raise ValueError(
+                "Cannot replace one element with another when the"
+                "element to be replaced is not part of a tree.")
         if replace_with is self:
             return
         if replace_with is self.parent:
@@ -228,6 +232,10 @@ class PageElement(object):
 
     def unwrap(self):
         my_parent = self.parent
+        if not self.parent:
+            raise ValueError(
+                "Cannot replace an element with its contents when that"
+                "element is not part of a tree.")
         my_index = self.parent.index(self)
         self.extract()
         for child in reversed(self.contents[:]):
@@ -667,7 +675,8 @@ class NavigableString(unicode, PageElement):
         """
         if isinstance(value, unicode):
             return unicode.__new__(cls, value)
-        return unicode.__new__(cls, value, DEFAULT_OUTPUT_ENCODING)
+        u = unicode.__new__(cls, value, DEFAULT_OUTPUT_ENCODING)
+        u.setup()
 
     def __copy__(self):
         return self
diff --git a/bs4/tests/test_tree.py b/bs4/tests/test_tree.py
index bab73c6..0bd4713 100644
--- a/bs4/tests/test_tree.py
+++ b/bs4/tests/test_tree.py
@@ -9,6 +9,7 @@ same markup, but all Beautiful Soup trees can be traversed with the
 methods tested here.
 """
 
+from pdb import set_trace
 import copy
 import pickle
 import re
@@ -780,6 +781,14 @@ class TestTreeModification(SoupTest):
         new_a = a.unwrap()
         self.assertEqual(a, new_a)
 
+    def test_replace_with_and_unwrap_give_useful_exception_when_tag_has_no_parent(self):
+        soup = self.soup("<a><b>Foo</b></a><c>Bar</c>")
+        a = soup.a
+        a.extract()
+        self.assertEqual(None, a.parent)
+        self.assertRaises(ValueError, a.unwrap)
+        self.assertRaises(ValueError, a.replace_with, soup.c)
+
     def test_replace_tag_with_itself(self):
         text = "<a><b></b><c>Foo<d></d></c></a><a><e></e></a>"
         soup = self.soup(text)