为什么python“（hash）.values（）”会给出“（hash）.keys（）没有给出的错误？

Question

I'm a beginner in python. Still studying basics. I tried below code and it gave me the expected result.

result_f=open("results.txt")
scores={}
for line in result_f:
    (name, score)=line.split()
    scores[score]=name
result_f.close()
for each in sorted(scores.keys(), reverse=True):
    print(each+' '+scores[each])

But if i use

scores.values()

instead of

scores.keys()

it will give me an error like this

" Traceback (most recent call last):

File "E:\\Practise for MYSELF\\Python\\TEST.py", line 8, in

print(each+' '+scores[each])

KeyError: 'Zack' "

Contents of "result.txt" file are

Johnny 8.65

Juan 9.12

Joseph 8.45

Stacey 7.81

Aideen 8.05

Zack 7.21

Aaron 8.31

please explain me, why does that error occur and how to fix it?

Answer 1

Dictionary lookup the value by key, not key by its value. The scores.keys() return the keys of the dict, while scores.values() return the values. Then scores[key] is getting the value using the key, so in this case the scores dictionary doesn't have the key Zack . Instead, Zack is a value.

Answer 2

When you switch scores.keys() to scores.values() , now the variable each doesn't store scores (numbers) like it used to. Instead, it stores names (strings) which can't be used inside the [] operator to look up values in the array.

What you probably wanted to do instead is have the loop go through every possible name and find the score associated with it. However, in order to do this you don't change the loop, you change the array.

To do this, the only line you need to change is scores[score]=name . Try changing it to scores[name]=score . This will now store the names as keys and the scores as values. If you run the code below, you will see that instead of having scores first and then names, you will have names first and then scores like I'm assuming you want. This matches the format of the input file you posted.

result_f=open("results.txt")
scores={}
for line in result_f:
    (name, score)=line.split()
    scores[name]=score
result_f.close()
for each in sorted(scores.keys(), reverse=True):
    print(each+' '+scores[each])