Added PY2, PY3 to compat module

lib/compat.py

@@ -4,12 +4,16 @@ __all__ = ['string_types', 'text_type', 'lru_cache']
 
 if sys.version_info[0] == 2:
     # Python 2
+    PY2 = True
+    PY3 = False
     string_types = basestring,
     text_type = unicode
     from ._lru_cache import lru_cache
 
 else:
     # Python 3
+    PY2 = False
+    PY3 = True
     string_types = str,
     text_type = str
     from functools import lru_cache