title: In Python, what does dict.pop(a,b) mean?
body: <pre><code>class a(object):
      data={'a':'aaa','b':'bbb','c':'ccc'}
      def pop(self, key, *args):
              return self.data.pop(key, *args)#what is this mean.
  
  b=a()
  print b.pop('a',{'b':'bbb'})
  print b.data
  </code></pre>
  
  <p><code>self.data.pop(key, *args)</code> &larr;------ why is there a second argument?</p>