Alternating-direction tuple sort with key function in python

Question

I need to sort a list of tuples (length 2) but specifically need it to sort by second value descending and then by first value ascending. i.e. (0,1)<(1,1)<(1,0)

I think I could do it without too much trouble with a comparison function, but would like to know if it's doable with a key function.

Answer 1

You could use a lambda key as follows:

tlist = [
    (1,1),
    (0,1),
    (1,0)
]

print(sorted(tlist, key=lambda x: (-x[1], x[0])))

Output:

[(0, 1), (1, 1), (1, 0)]

Or, without lambda...

def cf(t):
    a, b = t
    return -b, a

print(sorted(tlist, key=cf))