Python3中的排序字典

Question

I am working on an assignment for school. My professor gave us some code in class and im not sure how the logic of it works.

#wdcnt is dictionary with key = "some_string" and value = some_int
v = [wdcnt.values()]
v.sort()
for k in sorted(wdcnt, key = wdcnt.get, reverse = True):
    print(k,wdcnt[k])

1. I understand the premise of storing values into a list then sorting them, but why is v not used in the for loop. That line of code seems pointless as v is never used after.

2. wdcnt.get does not have "()" or parameters but still works to return a key value associated with k.

Please help me understand the logic behind this code fragment, thanks.

Note* the assignment is finished and works but to better understand I'd like to get the logic.

Answer 1

1. v Is not used later, you can ignore it, it is indeed useless for the loop

2. The argument wdcnt.get is used without parenthesis as it's passing the function as an argument (this is legal in Python):

From the docs :

key specifies a function of one argument that is used to extract a comparison key from each element in iterable (for example, key=str.lower). The default value is None (compare the elements directly).

Answer 2

1. I understand the premise of storing values into a list then sorting them, but why is v not used in the for loop. That line of code seems pointless as v is never used after.

That's right. Like khelwood said, v is unused and has no effect.

2. wdcnt.get does not have "()" or parameters but still works to return a key value associated with k.

wdcnt.get is the dictionary's .get method . wdcnt.get(k) is another way of saying wdcnt[k] .

In detail:

1. sorted iterates over the keys of wdcnt.
2. For each key k, sorted calls the specified key comparator wdcnt.get on it.
3. wdcnt.get(k) returns the word count value associated with k. sorted then uses those values to determine how to order of the keys.

Answer 3

The first two lines are unnecessary. It does not need to be used. sorted built-in is a function and one of its parameters is key. The key parameter determines how the array given to the sorted function will be sorted. It is only the name of the function given to the key. () is not used.