There are a few BPy functions that are documented to return a list but actually return tuples.

Blender.sys.splitext() raises an error if the path is longer then 80 chars. seems a bit short, noted this anyhow end added an example.
(hope its okay to do small doc corrections as I notice them.)

source/blender/python/api2_2x/doc/Sys.py

@@ -75,11 +75,20 @@ def join (dir, file):
 
 def splitext (path):
   """
-  Split 'path' into (root, ext), where 'ext' is a file extension.
+  Split 'path' into (root, ext), where 'ext' is a file extension including the full stop.
+
+  Example::
+
+    import Blender
+    file, ext= Blender.sys.splitext('/tmp/foobar.blend')
+    print file, ext
+    # ('/tmp/foobar', '.blend')
+
   @type path: string
   @param path: a path name
-  @rtype: list with two strings
+  @rtype: tuple of two strings
   @return: (root, ext)
+  @note: This function will raise an error if the path is longer then 80 characters.
   """
 
 def makename (path = "Blender.Get('filename')", ext = "", strip = 0):