@read_only<EOL><INDENT>def watch_method(self, method_name, callback):<DEDENT>
<EOL>try:<EOL><INDENT>method = getattr(self, method_name)<EOL><DEDENT>except AttributeError:<EOL><INDENT>raise ApiUsageError("""<STR_LIT>""")<EOL><DEDENT>if not isinstance(method, Token.WatchedMethod):<EOL><INDENT>setattr(self, method_name, Token.WatchedMethod(method))<EOL>method = getattr(self, method_name)<EOL><DEDENT>method.add_watcher(callback)<EOL>
Register the given callback to be called whenever the method with the 
given name is called.  You can easily take advantage of this feature in 
token extensions by using the @watch_token decorator.