title: if not info.new_interface(): TypeError: 'str' object is not callable, although i have used correct syntax of str
body: <pre><code>import subprocess
  import optparse
  
  
  def mac_changer(interface, mac_add):
      subprocess.call(&quot;ifconfig&quot; + str(interface)+&quot; down&quot;, shell=True)
      subprocess.call(&quot;ifconfig&quot; + str(interface)+&quot; hw ether &quot; + str(mac_add), shell=True)
      subprocess.call(&quot;ifconfig&quot; + str(interface)+&quot; up&quot;, shell=True)
  
  
  def get_args():
      parser = optparse.OptionParser()
      parser.add_option(&quot;-i&quot;, &quot;--interface&quot;, dest=&quot;new_interface&quot;, help=&quot;Selects Interface&quot;)
      parser.add_option(&quot;-m&quot;, &quot;--MAC&quot;, dest = &quot;new_mac&quot;, help=&quot;Changes the Mac Address&quot;)
      (options, arguments) = parser.parse_args()
      if not options.new_interface():
          parser.error(&quot;No interface specified&quot;)
      elif not options.new_mac:
          parser.error(&quot;No Mac address found in command line&quot;)
  
      return options
  
  
  options = get_args()
  mac_changer(options.interface, options.new_mac)
  </code></pre>
  <p>I have been working on a mac changer recently and it returns this this error, even though i do not use str function the entire code except when it's needed.</p>