Sorting names by their high scores

python, python-3.x, sorting

Solution

you can use the `.split(',')` method to split a line into its separate parts, then use `int()` to convert the score to a number. The `.sort()` method sorts a list in place, and the `key` tells it what to sort by.

scores = []
with open("scores.txt") as f:
    for line in f:
        name, score = line.split(',')
        score = int(score)
        scores.append((name, score))

scores.sort(key=lambda s: s[1])

for name, score in scores:
    print(name, score)

This will give you a list of tuples containing (name, score) pairs in sorted order. If you want to print them out with a comma in between them (to keep it consistent) change the print to `print(name, score, sep=', ')`

The reading of the input file can also be expressed as one (big) line

with open("scores.txt") as f:
    scores = [(name, int(score)) for name, score in (line.split(',') for line in f)]

A brief explanation of the `key=`:

a lambda function is an anonymous function, that is, a function without a name. You generally use these when you need a function only for a small operation. `.sort` has an optional `key` keyword argument that takes a function and uses the return of that function in sorting the objects.

So this `lambda` could also be written as

def ret_score(pair):
    return pair[1]

And you could then write `.sort(key=ret_score)` but since we dont really need that function for anything else, its not necessary to declare it. The lambda syntax is

lambda <arguments> : <return value>

So this lambda takes a pair, and returns the second element in it. You can save a `lambda` and use it like a regular function if you wish.

>>> square = lambda x: x**2 # takes x, returns x squared
>>> square(3)
9
>>> square(6)
36

Problem

Original source