Add missing docstring for BadTTL exception.

diff --git a/dns/ttl.py b/dns/ttl.py
index ab6ddf4e6659b95b3a679d7e4c53a38e4281357c..dc92b2146d728ce4f0c85d777b324ac52fe8a3bc 100644 (file)
--- a/dns/ttl.py
+++ b/dns/ttl.py
@@ -18,7 +18,7 @@
 import dns.exception
 
 class BadTTL(dns.exception.SyntaxError):
-    pass
+    """DNS TTL value is not well-formed."""
 
 def from_text(text):
     """Convert the text form of a TTL to an integer.