Comp Sci Reverse Dictionary Keys: d={1:7,2:5,3:7,4:16,5:25,6:5,9:7}

[ver_mathstats]

Homework Statement

Given a dictionary d, create a new dictionary that reverses the keys and values of d. Thus, the keys of d become the values of the new dictionary and the values of d become the keys of the new dictionary. If there is a common value for several keys in d then only the last key becomes a value in the new dictionary. Perform the following test case: when d is {1:7, 2:5, 3:7, 4:16, 5:25, 6:5, 9:7} your code should produce the dictionary {7:9, 5:6, 16:4, 25:5}.

Relevant Equations

python

d={1:7,2:5,3:7,4:16,5:25,6:5,9:7}
reverse_d={}
for a, b in d.items():
    reverse_d[b] = reverse_d.get(b,a)
print(reverse_d)

I ended up reversing the keys in the dictionary, so I have the 7, 5, 16, and 25 correct. I am just struggling with making the last key become a new value in the dictionary. Overall my code prints {7:1, 5:2, 16:4, 25:5}, I just do not know how to get the last element. Could I please have help with that? Thank you.

 

[DaveC426913]

my code prints {7:1, 5:2, 16:4, 25:5}

Maybe I'm misunderstanding but it looks like the bug is occurring earlier than 9:7. It's occurring at 3:7.

"If there is a common value for several keys in d then only the last key becomes a value in the new dictionary. "

Your output should at least be 7:3, not 7:1.

I am not sure how to fix it but I suspect that you need to create a new, updated d each iteration. I think, currently, you're always operating on the initial d.

 

[pbuk]

    reverse_d[b] = reverse_d.get(b,a)

What does this do if the key b already exists? What do you want it to do?

Think simpler (I can't help thinking that you have copied the get() from the answer to a different and harder problem).

 

[ver_mathstats]

    reverse_d[b] = reverse_d.get(b,a)

What does this do if the key b already exists? What do you want it to do?

Think simpler (I can't help thinking that you have copied the get() from the answer to a different and harder problem).

https://www.w3schools.com/python/python_dictionaries.asp here's the website we were given to use so I thought I would use the get().

 

[ver_mathstats]

Maybe I'm misunderstanding but it looks like the bug is occurring earlier than 9:7. It's occurring at 3:7.

"If there is a common value for several keys in d then only the last key becomes a value in the new dictionary. "

Your output should at least be 7:3, not 7:1.

I am not sure how to fix it but I suspect that you need to create a new, updated d each iteration. I think, currently, you're always operating on the initial d.

Yes I see, that makes sense. Thank you.

 

[pbuk]

Yes I see, that makes sense. Thank you.

No, that is not the answer, you just need to follow through your code and work out what it does when it gets to 3:7.

 

[pbuk]

No, that is not the answer, you just need to follow through your code and work out what it does when it gets to 3:7.

...so I thought I would use the get().

But at 3:7, do you want to know the current value of reverse_d[7]?