title: Pandas series.rename gives TypeError: 'str' object is not callable error
body: <p>I can't figure out why this happens. I know this could happen if I have the function name "shadowed" somehow. But how could I in this scenario? </p>
  
  <p>If I open iPython in my terminal and then type:</p>
  
  <pre><code>import pandas as pd
  a = pd.Series([1,2,3,4])
  a.rename("test")
  </code></pre>
  
  <p>I get TypeError: 'str' object is not callable. What could be the causes of this?</p>
  
  <p>Longer error msg:</p>
  
  <pre><code>   /usr/local/lib/python2.7/site-packages/pandas/core/series.pyc in rename(self, index, **kwargs)
     2262     @Appender(generic._shared_docs['rename'] % _shared_doc_kwargs)
     2263     def rename(self, index=None, **kwargs):
  -&gt; 2264         return super(Series, self).rename(index=index, **kwargs)
     2265
     2266     @Appender(generic._shared_docs['reindex'] % _shared_doc_kwargs)
  
  /usr/local/lib/python2.7/site-packages/pandas/core/generic.pyc in rename(self, *args, **kwargs)
      604
      605             baxis = self._get_block_manager_axis(axis)
  --&gt; 606             result._data = result._data.rename_axis(f, axis=baxis, copy=copy)
      607             result._clear_item_cache()
      608
  
  /usr/local/lib/python2.7/site-packages/pandas/core/internals.pyc in rename_axis(self, mapper, axis, copy)
     2586         """
     2587         obj = self.copy(deep=copy)
  -&gt; 2588         obj.set_axis(axis, _transform_index(self.axes[axis], mapper))
     2589         return obj
     2590
  
  /usr/local/lib/python2.7/site-packages/pandas/core/internals.pyc in _transform_index(index, func)
     4389         return MultiIndex.from_tuples(items, names=index.names)
     4390     else:
  -&gt; 4391         items = [func(x) for x in index]
     4392         return Index(items, name=index.name)
     4393
  </code></pre>
  
  <p>Reference for test example <a href="http://pandas.pydata.org/pandas-docs/stable/generated/pandas.Series.rename.html" rel="noreferrer">here</a>.</p>