Changed default parameter checking and added some docs

README.md

@@ -3,7 +3,6 @@ python-libsmpp
 
 SMPP library for Python. Forked from [google code](https://code.google.com/p/smpplib/).
 
-
 Example:
 ```python
 import logging
@@ -53,5 +52,15 @@ t = Thread(target=client.listen)
 t.start()
 ```
 
+The client supports setting a custom generator that produces sequence numbers for the PDU packages. Per default a simple in memory generator is used which in conclusion is reset on (re)instantiation of the client, e.g. by an application restart. If you want to keep the sequence number to be persisted across restarts you can implement your own storage backed generator.
+
+Example:
+```
+import smpplib.client
 
+import mymodule
 
+generator = mymodule.PersistentSequenceGenerator()
+client = smpplib.client.Client('example.com', SOMEPORTNUMBER, sequence_generator=generator)
+...
+```

smpplib/client.py

@@ -71,7 +71,9 @@ def __init__(self, host, port, timeout=5, sequence_generator=None):
         self._socket = socket.socket(socket.AF_INET, socket.SOCK_STREAM)
         self._socket.settimeout(timeout)
         self.receiver_mode = False
-        self.sequence_generator = sequence_generator or SimpleSequenceGenerator()
+        if sequence_generator is None:
+            sequence_generator = SimpleSequenceGenerator()
+        self.sequence_generator = sequence_generator
 
     def __del__(self):
         """Disconnect when client object is destroyed"""