sort_key_demo.py

from collections import namedtuple
Key = namedtuple('Key', ['index', 'ascending'])
keys = [Key(index=2, ascending=False), Key(index=0, ascending=True)]
def sort_key(row):
    values = []
    for key in keys:
        value = converted(row[key.index])
        values.append(value if key.ascending else -value)
    return tuple(values)
print(sort_key([1, 2, 3, 4]))
# Output: (-3, 1)