'Return the position of col_name in self.columns.
Parameters
col_name : str
Name of column to look up'

def col_position(self, col_name):

    for (i, c) in enumerate(self.columns):
        if (c.info.name == col_name):
            return i
    raise ValueError(u'Column    does    not    belong    to    index:    {0}'.format(col_name))
