Added error handling for range mode

Author: seanlaw

versions.py

@@ -479,6 +479,8 @@ def get_all_min_versions(MIN_PYTHON):
  elif args.mode == "max":
  get_all_max_versions()
  elif args.mode == "range":
+ if len(args.python_version) <= 2:
+ raise IndexError("Please provide both a start and stop version")
  start = args.python_version[0]
  stop = args.python_version[1]
  get_all_python_versions_in_range(start, stop)