Pandas - group by

The dataset contains climate data, the data structure is:

year	month	temp max	temp min	air frost	rain (mm)	hours of sunshine
1948	1	6.6	1.3	8	170.8	40.1

I want to visualise the total hours of sunshine for the summer months (June, July, August) per year. The steps involved in preparing the data were:

1. keep only months 6, 7 and 8, so create a subset of the full dataframe
2. drop unnecessary columns - reduces computing power required 
3. group by year and sum

the code:

The data can then be plotted.

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