title: difference between `header = None` and `header = 0` in pandas
body: <p>I was writing a code to read a <code>csv</code> file using <code>pandas</code> and I saw some weird functioning of the package. My file has column names which I want to ignore, so I use <code>header = 0</code> or <code>'infer'</code> instead of <code>None</code>. But I see something weird.</p>
  
  <p>When I use <code>None</code> and I want to get a specific column, I just need to do <code>df[column_index]</code> but when I use <code>0</code> or <code>'infer'</code>, I need to do <code>df.ix[:,column_index]</code> to get the column otherwise, for <code>df[column_index]</code> I get the following error:</p>
  
  <blockquote>
    <p>Traceback (most recent call last):   File
    "/home/sarvagya/anaconda3/envs/tf/lib/python3.6/site-packages/pandas/core/indexes/base.py",
    line 2525, in get_loc
        return self._engine.get_loc(key)   File "pandas/_libs/index.pyx", line 117, in pandas._libs.index.IndexEngine.get_loc   File
    "pandas/_libs/index.pyx", line 139, in
    pandas._libs.index.IndexEngine.get_loc   File
    "pandas/_libs/hashtable_class_helper.pxi", line 1265, in
    pandas._libs.hashtable.PyObjectHashTable.get_item   File
    "pandas/_libs/hashtable_class_helper.pxi", line 1273, in
    pandas._libs.hashtable.PyObjectHashTable.get_item KeyError: column_index</p>
    
    <p>During handling of the above exception, another exception occurred:</p>
    
    <p>Traceback (most recent call last):   File "", line 1, in
       File
    "/home/sarvagya/anaconda3/envs/tf/lib/python3.6/site-packages/pandas/core/frame.py",
    line 2139, in <strong>getitem</strong>
        return self._getitem_column(key)   File "/home/sarvagya/anaconda3/envs/tf/lib/python3.6/site-packages/pandas/core/frame.py",
    line 2146, in _getitem_column
        return self._get_item_cache(key)   File "/home/sarvagya/anaconda3/envs/tf/lib/python3.6/site-packages/pandas/core/generic.py",
    line 1842, in _get_item_cache
        values = self._data.get(item)   File "/home/sarvagya/anaconda3/envs/tf/lib/python3.6/site-packages/pandas/core/internals.py",
    line 3843, in get
        loc = self.items.get_loc(item)   File "/home/sarvagya/anaconda3/envs/tf/lib/python3.6/site-packages/pandas/core/indexes/base.py",
    line 2527, in get_loc
        return self._engine.get_loc(self._maybe_cast_indexer(key))   File "pandas/_libs/index.pyx", line 117, in
    pandas._libs.index.IndexEngine.get_loc   File
    "pandas/_libs/index.pyx", line 139, in
    pandas._libs.index.IndexEngine.get_loc   File
    "pandas/_libs/hashtable_class_helper.pxi", line 1265, in
    pandas._libs.hashtable.PyObjectHashTable.get_item   File
    "pandas/_libs/hashtable_class_helper.pxi", line 1273, in
    pandas._libs.hashtable.PyObjectHashTable.get_item KeyError: column_index</p>
  </blockquote>
  
  <p>Can someone help with this? Why is this happening?</p>