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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 user_exists(name,
                user=None, host=None, port=None, maintenance_db=None,
                password=None,
                runas=None):
    '''
    Checks if a user exists on the Postgres server.

    CLI Example:

    .. code-block:: bash

        salt '*' postgres.user_exists 'username'
    '''
    return bool(
        role_get(name,
                 user=user,
                 host=host,
                 port=port,
                 maintenance_db=maintenance_db,
                 password=password,
                 runas=runas,
                 return_password=False))