如何在Python3中使用sum函数

Question

I'm trying to use the sum function multiple times after one another but I keep getting a error message. I wrote the following code:

averages["averages_home_goals"] = sum(d['home_goals'] for d in averages.values() if d)
averages["averages_away_goals"] = sum(d['away_goals'] for d in averages.values() if d)
averages["averages_home_conceded"] = sum(d['home_conceded'] for d in averages.values() if d)
averages["averages_away_conceded"] = sum(d['away_conceded'] for d in averages.values() if d)

print(averages)

The averages variable looks like the following:

{
    'Belconnen%20United': {
        'home_goals': 4.0,
        'away_goals': 1.0,
        'home_conceded': 0.0,
        'away_conceded': 2.1666666666666665,
    },
    'Canberra%20FC': {
        'home_goals': 1.75,
        'away_goals': 1.8,
        'home_conceded': 2.0,
        'away_conceded': 2.0,
    },
    # More data of a similar structure
}

When I run this I get the following error:

TypeError: 'float' object is not subscriptable

The weird thing is; when I run only one of these 4 lines the code executes fine (I doesn't matter which line). I'm getting the error upon executing the averages["averages_away_goals"] = ... statement

Could anyone help me out? Giving variable d another name also doesn't work

Answer 1

The first line will work just fine, but the failing will start on the second line and continues onwards. The reason is that you have included a new entry in the averages dictionary after the first line. Hence your averages dictionary has a new key "averages_home_goals" with a single float value.

When you execute the second line, you iterate through all the values of the dictionary averages , which now has an additional value of the sum of all home goals in the key "averages_home_goals" , which is going to be a float. And you cannot subscript a float. Basically what it means that you are trying to execute an example of a code (on the second line) of these sorts:

12.3242["away_goals"]

which will always fail.

As a solution I'd suggest to store the results into a new dictionary, fe

res = {}

res["averages_home_goals"] = sum(d['home_goals'] for d in averages.values() if d)
res["averages_away_goals"] = sum(d['away_goals'] for d in averages.values() if d)
res["averages_home_conceded"] = sum(d['home_conceded'] for d in averages.values() if d)
res["averages_away_conceded"] = sum(d['away_conceded'] for d in averages.values() if d)

print(res)