diff --git a/tftpy/TftpServer.py b/tftpy/TftpServer.py
index 364227c..0f15fc0 100644
--- a/tftpy/TftpServer.py
+++ b/tftpy/TftpServer.py
@@ -28,8 +28,11 @@ class TftpServer(TftpSession):
         # A dict of sessions, where each session is keyed by a string like
         # ip:tid for the remote end.
         self.sessions = {}
-
-        if os.path.exists(self.root):
+        
+        if self.dyn_file_func:
+            if not callable(self.dyn_file_func):
+                raise TftpException, "A dyn_file_func supplied, but it is not callable."
+        elif os.path.exists(self.root):
             log.debug("tftproot %s does exist" % self.root)
             if not os.path.isdir(self.root):
                 raise TftpException, "The tftproot must be a directory."
diff --git a/tftpy/__init__.py b/tftpy/__init__.py
index e8ef87f..fba9a9f 100644
--- a/tftpy/__init__.py
+++ b/tftpy/__init__.py
@@ -11,14 +11,15 @@ directly. The TftpClient and TftpServer classes can be reached through it.
 import sys
 
 # Make sure that this is at least Python 2.3
-verlist = sys.version_info
-if not verlist[0] >= 2 or not verlist[1] >= 3:
-    raise AssertionError, "Requires at least Python 2.3"
+required_version = (2, 3)
+if sys.version_info < required_version:
+    raise ImportError, "Requires at least Python 2.3"
+
+from tftpy.TftpShared import *
+from tftpy.TftpPacketTypes import *
+from tftpy.TftpPacketFactory import *
+from tftpy.TftpClient import *
+from tftpy.TftpServer import *
+from tftpy.TftpContexts import *
+from tftpy.TftpStates import *
 
-from TftpShared import *
-from TftpPacketTypes import *
-from TftpPacketFactory import *
-from TftpClient import *
-from TftpServer import *
-from TftpContexts import *
-from TftpStates import *