docstr: Generate a response to the user input.
  
  :type str: str
  :param str: The string to be mapped
  :rtype: str
code: def respond(self, str):
      """
      Generate a response to the user input.
  
      :type str: str
      :param str: The string to be mapped
      :rtype: str
      """
  
      # check each pattern
      for pattern, response in self._pairs:
          match = pattern.match(str)
  
          # did the pattern match?
          if match:
              resp = random.choice(response)  # pick a random response
              resp = self._wildcards(resp, match)  # process wildcards
  
              # fix munged punctuation at the end
              if resp[-2:] == "?.":
                  resp = resp[:-2] + "."
              if resp[-2:] == "??":
                  resp = resp[:-2] + "?"
              return resp
  
file_path: nltk/nltk/chat/util.py
imports: import random
  import re
label_desc: Use image node_id 5 for calling the Chat obj's underlying member method code with example usage: obj.respond(str) and returns: resp