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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 run_export_db(filename=None):
 """ Exports the database on the server. Usage:: fab prod run_export_db fab prod run_export_db:filename=foobar.dump """

    if not filename:
        filename = settings.DB_DUMP_FILENAME
    with cd(settings.FAB_SETTING('SERVER_PROJECT_ROOT')):
        run_workon('fab export_db:remote=True,filename={}'.format(filename))