- String2Key count is a single octet, so the

value must be constrained to the range
  0-255 inclusive
- reversed six.PY2/3 checks so six.PY2 is the special case
- singledispatch import now tries the one in functools if singledispatch is not installed

pgpy/decorators.py

@@ -5,7 +5,12 @@ import functools
 import six
 import warnings
 
-from singledispatch import singledispatch
+try:
+    from singledispatch import singledispatch
+
+except ImportError:
+    from functools import singledispatch
+
 
 from .errors import PGPError