only import readline module when starting interactive prompt

comment.py

@@ -18,7 +18,6 @@ __status__ = "Prototype"
 import antlr4
 import configparser
 import logging
-import readline
 import sys
 
 from CommentMacroLexer import CommentMacroLexer
@@ -62,6 +61,7 @@ if __name__ == '__main__':
         logger.debug("found macro at argv[1]")
         comment(sys.argv[1])
     else:
+        import readline     # for input history and line editing
         while True:
             try:
                 text = input("comment# ")