Increment value of integer in Python dictionary

Question

So I write an app that counts amount of yellow cards in football matches through all the games of the tournament. So let's say I count all Brazil's goals and I need to increment the amount of yellow cards with each game I go through in a loop. So I have this dictionary cards_per_team_dictionary that looks like this:

['Brazil', 0]

and I wan't to increment the int value with each game. I tried the following but it doesn't seem to work:

def add_yellow_cards_per_team(team_name, cards_num):
    cards_per_team_dictionary[team_name] += cards_num

I get an error:

cards_per_team_dictionary[team_name] += cards_num TypeError: 'set' object is not subscriptable 

And also this:

def add_yellow_cards_per_team(team_name, cards_num):
    cards_per_team_dictionary[team_name] + cards_num

But it seems to overrun the previous integer instead of adding up to it. Thanks in advance!

Answer 1

You have created a set not a dict:

In [4]: d = {"Brazil",0}

In [5]: d["Brazil"] += 3
---------------------------------------------------------------------------
TypeError                                 Traceback (most recent call last)
<ipython-input-5-8db3ec29e78a> in <module>()
----> 1 d["Brazil"] += 3

TypeError: 'set' object is not subscriptable

To create a dict, you add key/value pairs separated by a colon i.e key:value:

In [6]: d = {"Brazil":0}

In [7]: d["Brazil"] += 3

In [8]: d
Out[8]: {'Brazil': 3}

Both a dict and set literals use {}, one difference being d = {} creates an empty dict where st = set() is needed to create an empty set.

If you want to add a key value pairing:

 d[key] = value

But for repeating keys you can use dict.setdefault:

data = [("Brazil", 4),("Argentina",6)]
d = {}
for team, count in data:
    d.setdefault(team, 0)
    d[team] += count

A more efficient option is to use a defauldict:

from collections import defaultdict
d = defaultdict(int)
for team, count in data:
    d[team] += count

In both cases if the key does not exist it is added with the new value, if it does exist the value for the key is increased.