Add words discouraging overly-broad except clauses.

pep-0008.txt

@@ -689,6 +689,28 @@ Programming Recommendations
             the exception propagate upwards with 'raise'.
             'try...finally' is a better way to handle this case.
 
+    - Additionally, for all try/except clauses, limit the 'try' clause
+      to the absolute minimum amount of code necessary.  Again, this
+      avoids masking bugs.
+
+      Yes:
+
+          try:
+              value = collection[key]
+          except KeyError:
+              return key_not_found(key)
+          else:
+              return handle_value(value)
+
+      No:
+
+          try:
+              # Too broad!
+              return handle_value(collection[key])
+          except KeyError:
+              # Will also catch KeyError raised by handle_value()
+              return key_not_found(key)
+
     - Use string methods instead of the string module.
 
       String methods are always much faster and share the same API with