sqlalchemy dynamic mapping

I have the following problem:

I have the class:

class Word(object):

    def __init__(self):
        self.id = None
        self.columns = {}

    def __str__(self):
        return "(%s, %s)" % (str(self.id), str(self.columns))

self.columns is a dict which will hold (columnName:columnValue) values. The name of the columns are known at runtime and they are loaded in a wordColumns list, for example

wordColumns = ['english', 'korean', 'romanian']

wordTable = Table('word', metadata,
                  Column('id', Integer, primary_key = True)
                  )
for columnName in wordColumns:
    wordTable.append_column(Column(columnName, String(255), nullable = False))

I even created a explicit mapper properties to "force" the table columns to be mapped on word.columns[columnName], instead of word.columnName, I don't get any error on mapping, but it seems that doesn't work.

mapperProperties = {}
for column in wordColumns:
    mapperProperties['columns[\'%']' % column] = wordTable.columns[column]

mapper(Word, wordTable, mapperProperties)

When I load a word object, SQLAlchemy creates an object which has the word.columns['english'], word.columns['korean'] etc. properties instead of loading them into word.columns dict. So for each column, it creates a new property. Moreover word.columns dictionary doesn't even exists.

The same way, when I try to persist a word, SQLAlchemy expects to find the column values in properties named like word.columns['english'] (string type) instead of the dictionary word.columns.

I have to say that my experience with Python and SQLAlchemy is quite limited, maybe it isn't possible to do what I'm trying to do.

Any help appreciated,

Thanks in advance.