How to do a string plus string operation in Dictionary condition in python?

Question

My function is like

def calResult(w,t,l,team):
    wDict={}
    for item in team:
        for x in w:
            wDict[item]=int(wDict[item])+int(x[item.index(" "):item.index(" ")+1])
        for x in t:
            wDict[item]=int(wDict[item])+int(x[item.index(" "):item.index(" ")+1])
    return wDict

say I create the empty dict then I use wDict[item] to assign value for each key(these are from a team list, we have team like abc d...). the x[item.index(" "):item.index(" ")+1] part will return a value after the int method have run. But the python shell returned that

Traceback (most recent call last):
  File "C:\Program Files (x86)\Wing IDE 101 4.1\src\debug\tserver\_sandbox.py", line 66, in <module>
  File "C:\Program Files (x86)\Wing IDE 101 4.1\src\debug\tserver\_sandbox.py", line 59, in calResult
builtins.KeyError: 'Torino'

I can't understand what exactly is the error in my code.

Answer 1

I'm not quite sure what you're trying to do here (consider using more descriptive variable names than x , for starters), but here is the problem:

wDict[item]=int(wDict[item])+...

The first time you do this, wDict[item] doesn't exist, hence the KeyError .

What you want, I think, is:

wDict[item] = wDict.get(item, 0) + int(x[item.index(" "):item.index(" ")+1])

.get() takes a key and a default value to use if that key doesn't exist.

You might also want to use the Counter class in collections , which is designed to default nonexistent keys to zero for just this sort of situation.

Answer 2

You can not access wDict[item] the first time, since your dict is empty

This would be ok:

wDict[item] = 1

But you can not do this :

wDict[item] = wDict[item] + 1

Maybe you want to use this syntax :

wDict[item] = int(wDict.get(item, 0)]) + int(x[item.index(" "):item.index(" ") + 1])

Answer 3

Looks like you are trying to use wDict[item] as the rvalue and the lvalue in the same assignment statement, when wDict[item] is not yet initialized.

wDict[item]=int(wDict[item])+int(x[item.index(" "):item.index(" ")+1])

You are trying to access the "value" of the key item, but there is no key value pair initialized.