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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 change_password(username, password, uid=None):
    '''
    Change users password

    CLI Example:

    .. code-block:: bash

        salt dell drac.change_password [USERNAME] [PASSWORD] [UID - optional]
        salt dell drac.change_password diana secret
    '''
    if uid is None:
        user = list_users()
        uid = user[username]['index']

    if uid:
        return __execute_cmd('config -g cfgUserAdmin -o \
                cfgUserAdminPassword -i {0} {1}'.format(uid, password))
    else:
        log.warning('\'%s\' does not exist', username)
        return False

    return True