How to generate random numbers that are unique forever in python

I have written a script where I need a unique random number every time I run that script. Just for explaination: suppose that I want my script 5 times. Now I want number generated in all times should be unique?

I have found a lot of infomation about random number uniqueness but those are for one time only. If you think it is not possible then is there any alternative way etc.?