Number list with no repeats and ordered

Question

This code returns a list [0,0,0] to [9,9,9], which produces no repeats and each element is in order from smallest to largest.

def number_list():
    b=[]
    for position1 in range(10):
        for position2 in range(10):
            for position3 in range(10):
                if position1<=position2 and position2<=position3:
                    b.append([position1, position2, position3])

    return b

Looking for a shorter and better way to write this code without using multiple variables (position1, position2, position3), instead only using one variable i.

Here is my attempt at modifying the code, but I'm stuck at implementing the if statements:

def number_list():
    b=[]
    for i in range(1000):
        b.append(map(int, str(i).zfill(3)))
    return b

Answer 1

On the same note as the other itertools answer, there is another way with combinations_with_replacement:

list(itertools.combinations_with_replacement(range(10), 3))