Python使用append写入Tuple Error

Question

I'm practicing Python 3.3.2 and I would like to practice the append technique to a tuple.
I have a text file named user_scores.txt. and it consists of scores from people in my workplace that they have submitted for a mathematical problem. They have submitted different answers that they could produce. The file is shown below (Alex only submitted two):

Alex, 35, 39
Daniel, 34, 35, 36 
Richard, 21, 23, 24

I am trying to write these scores to a tuple in this form:

Name:Score, Score, Score.

So for example:
Alex:35, 39,
Daniel:34, 35, 36

I have attempted this with the code below, but it does not work as it returns the error underneath:

user_scores = []

with open('user_scores.txt') as f:
    for line in f:
        worker,score = line.strip().replace("\n","").split(",")
        user_scores[worker].append(int(score))

The error:

ValueError: too many values to unpack (expected 2)

What is the fix? Is my block of code completely wrong or what?

Thanks, Dora.

Answer 1

First let's fix your data structure. You're referring to each score-tuple by test-taker name. Referring to values by a key (rather than by an index) is done using a dictionary.

user_scores = dict() # or = {}. Same difference.

Then we know two things:

1. That the first item each line will be the name of the test-taker
2. That there will be some number of scores thereafter, which will all be integers

So we can iterate through the file like this:

with open('path/to/file.txt') as infile:
    for line in infile:
        name, *scores = line.strip().split(',')

The glob there * instructs Python that there will be lots of these, so make a tuple of equivalent size. a, *b = (1, 2, 3, 4, 5) makes a = 1; b = (2, 3, 4, 5) a = 1; b = (2, 3, 4, 5) . Now it's an easy thing to assign your values!

user_scores[name] = [int(score) for score in scores]

Note that this creates a list, not a tuple, but that's LIKELY what you want anyway. Tuples indicate that the position of each element isn't just important but it HAS MEANING. This is easily explained by a point in the 2-D coordinate plane expressed as an ordered pair

#x, y
(1, 10)

is much different from

#x , y
(10, 1)

In a list, it might be important that the list keep its order, but all of the elements MEAN the same thing. That's your use case here -- they're all scores, and you might want to correlate that each test-taker improved over time, but ultimately if a test score got moved to a different position, it doesn't change the fact that it's still a test score.

Answer 2

It looks like you're trying to write to a list, not a tuple. Tuples are immutable, so this wouldn't be possible anyway. It also looks like you'd be trying to index the list by a string. This isn't possible, because lists require indexing by number. I think what you want is a dict.

Also, when you do

worker, score = [list of things]

python expects list of things to have 2 items in it. You're apparently going to have a variable number of things.

Try this:

user_scores = {}

with open('user_scores.txt') as f:
    for line in f:
        this_line = line.strip().replace("\n","").split(",")
        user_scores[this_line[0]] = this_line[1:]

This will create a dict that you can access by a person's name, and get back a list of their scores, no matter how many things are in the list. For each line, it will split all of the things in the line by commas, make the key the person's name, and make the value a list of their scores.

If you want the scores to be stored as numbers rather than strings, replace that last line with:

user_scores[this_line[0]] = [int(score) for score in this_line[1:]]

Using a list in this case is better than using a tuple to store the scores because one can append to a list, a mutable type, but not to a tuple, an immutable type.