code: def column_alias(cell, names):
      
      column = slugify(cell.column or '', sep='_')
      column = column.strip('_')
      column = 'column' if not len(column) else column
      name, i = column, 2
      # de-dupe: column, column_2, column_3, ...
      while name in names:
          name = '%s_%s' % (name, i)
          i += 1
      return name
docs: Generate a normalized version of the column name.