code: def email(prompt=None, empty=False, mode="simple"):
      
      if mode == "simple":
          s = _prompt_input(prompt)
          if empty and not s:
              return None
          else:
              if RE_EMAIL_SIMPLE.match(s):
                  return s
              else:
                  return email(prompt=prompt, empty=empty, mode=mode)
      else:
          raise ValueError
docs: Prompt an email address.
  
      This check is based on a simple regular expression and does not verify
      whether an email actually exists.
  
      Parameters
      ----------
      prompt : str, optional
          Use an alternative prompt.
      empty : bool, optional
          Allow an empty response.
      mode : {'simple'}, optional
          'simple' will use a simple regular expression.
          No other mode is implemented yet.
  
      Returns
      -------
      str or None
          A str if the user entered a likely email address.
          None if the user pressed only Enter and ``empty`` was True.