How can I build a weighted random list?

I'm writing a ranking algorithm and I would like to add randomness factor .

I'm generating a list of 10 items where each item has a value from 1 to 10 :

l = [random.randint(1,10) for num in range(1, 11)]

I'm running this code around 400 times and storing the large list in a DB .

I would like to add probability to it, so 70% of the times it generate radom numbers between 1 and 5 for the first 5 items, and 5 to 10 for the last 5 items .

And 30% of the times it stays random without any probability (normal mode) .

How can I achieve this using python and it's random module ?