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Solve the following problem using Python, implementing the functions described below, one line at a time
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Description:
 def AddTableColumns(self, table, columns):
 """Add columns to table if they are not already there. Args: table: table name as a string columns: an iterable of column names"""

    table_columns = self._table_columns.setdefault(table, [])
    for attr in columns:
      if attr not in table_columns:
        table_columns.append(attr)