Question

Hopefully I can explain what I am trying to accomplish. I have no problem achieving my result, but I know that this is probably not the best way to do it.

I have a table with some entries by date. I am trying to take those entries from the current month, and arrange them into a list by week, and then sum a value from the table for each day of the week. The end result would look something like this:

{44: {4: Decimal('2.80'), 5: Decimal('6.30')}, 45: {1: Decimal('8.90'), 2: Decimal('10.60')}}

I have a solution. But, I know this is not the best way to do it. Any ideas about how to make this better?

#Queries the database and returns time objects that have fields 'hours' and 'date'
time = self.month_time()

r = {}
for t in time:
    #Get the week of the year number
    week = t.date.isocalendar()[1]

    #Get the day of the week number
    day = t.date.isoweekday()

    if week not in r:
        r.update({week:{}})
    if day not in r[week]:
        r[week][day] = 0

    r[week][day] = r[week][day] + t.hours

Answer 1

I think you are probably looking for the defaultdict. A defaultdict is just like a dictionary, except when a KeyError would be thrown with dict, the factory function given upon initialization is used to create an initial value.

In your case, you’ll need a defaultdict for days nested inside one for weeks. I think this will work for you:

from collections import defaultdict

r = defaultdict(lambda: defaultdict(int))
for t in time:
    week = t.date.isocalendar()[1]
    day = t.date.isoweekday()
    r[week][day] += t.hours