A line of code is written once and read dozens of times: while debugging, while adding features, by teammates, and by you in six months when you've forgotten everything. Making code easy to read is not decoration; it's most of what makes software possible to maintain.

Names do more for readability than anything else. Compare:

def calc(l, t):
    r = []
    for x in l:
        if x[1] > t:
            r.append(x[0])
    return r

def names_above(scores, threshold):
    winners = []
    for name, score in scores:
        if score > threshold:
            winners.append(name)
    return winners

They do exactly the same thing. Only one of them can be understood without working it out.