code: def is_username(string, minlen=1, maxlen=15):
      
      if string:
          string = string.strip()
          return username_re.match(string) and (minlen <= len(string) <= maxlen)
      return False
docs: Determines whether the @string pattern is username-like
          @string: #str being tested
          @minlen: minimum required username length
          @maxlen: maximum username length
  
          -> #bool