diff -r bf6163635eda Doc/library/email.contentmanager.rst
--- a/Doc/library/email.contentmanager.rst	Sat Sep 20 11:53:12 2014 -0400
+++ b/Doc/library/email.contentmanager.rst	Sat Sep 20 16:57:04 2014 -0400
@@ -70,11 +70,15 @@
    the following methods:
 
 
-   .. attribute:: is_attachment
+   .. method:: is_attachment
 
-      Set to ``True`` if there is a :mailheader:`Content-Disposition` header
+      Return ``True`` if there is a :mailheader:`Content-Disposition` header
       and its (case insensitive) value is ``attachment``, ``False`` otherwise.
 
+      .. versionchanged:: 3.4.2
+         is_attachment is now a method instead of a property, for consistency
+         with :meth:`~email.message.Message.is_multipart`.
+
 
    .. method:: get_body(preferencelist=('related', 'html', 'plain'))
 
diff -r bf6163635eda Lib/email/message.py
--- a/Lib/email/message.py	Sat Sep 20 11:53:12 2014 -0400
+++ b/Lib/email/message.py	Sat Sep 20 16:57:04 2014 -0400
@@ -9,6 +9,7 @@
 import re
 import uu
 import quopri
+import warnings
 from io import BytesIO, StringIO
 
 # Intrapackage imports
@@ -929,6 +930,17 @@
     # I.e. def walk(self): ...
     from email.iterators import walk
 
+# XXX Support for temporary deprecation hack for is_attachment property.
+class _IsAttachment:
+    def __init__(self, value):
+        self.value = value
+    def __call__(self):
+        return self.value
+    def __bool__(self):
+        warnings.warn("is_attachment will be a method, not a property, in 3.5",
+                      DeprecationWarning,
+                      stacklevel=3)
+        return self.value
 
 class MIMEPart(Message):
 
@@ -941,12 +953,12 @@
     @property
     def is_attachment(self):
         c_d = self.get('content-disposition')
-        if c_d is None:
-            return False
-        return c_d.lower() == 'attachment'
+        # XXX transitional hack to raise deprecation if not called.
+        result = False if c_d is None else c_d.lower() == 'attachment'
+        return _IsAttachment(result)
 
     def _find_body(self, part, preferencelist):
-        if part.is_attachment:
+        if part.is_attachment():
             return
         maintype, subtype = part.get_content_type().split('/')
         if maintype == 'text':
@@ -1039,7 +1051,7 @@
         for part in parts:
             maintype, subtype = part.get_content_type().split('/')
             if ((maintype, subtype) in self._body_types and
-                    not part.is_attachment and subtype not in seen):
+                    not part.is_attachment() and subtype not in seen):
                 seen.append(subtype)
                 continue
             yield part
diff -r bf6163635eda Lib/test/test_email/test_message.py
--- a/Lib/test/test_email/test_message.py	Sat Sep 20 11:53:12 2014 -0400
+++ b/Lib/test/test_email/test_message.py	Sat Sep 20 16:57:04 2014 -0400
@@ -722,13 +722,21 @@
 
     def test_is_attachment(self):
         m = self._make_message()
-        self.assertFalse(m.is_attachment)
+        self.assertFalse(m.is_attachment())
+        with self.assertWarns(DeprecationWarning):
+            self.assertFalse(m.is_attachment)
         m['Content-Disposition'] = 'inline'
-        self.assertFalse(m.is_attachment)
+        self.assertFalse(m.is_attachment())
+        with self.assertWarns(DeprecationWarning):
+            self.assertFalse(m.is_attachment)
         m.replace_header('Content-Disposition', 'attachment')
-        self.assertTrue(m.is_attachment)
+        self.assertTrue(m.is_attachment())
+        with self.assertWarns(DeprecationWarning):
+            self.assertTrue(m.is_attachment)
         m.replace_header('Content-Disposition', 'AtTachMent')
-        self.assertTrue(m.is_attachment)
+        self.assertTrue(m.is_attachment())
+        with self.assertWarns(DeprecationWarning):
+            self.assertTrue(m.is_attachment)