Use type of first value as start argument for sum aggregator

[daviewales]

The sum aggregator uses Python's built-in sum function:

visidata/visidata/aggregators.py

Line 128 in 4ffacbb

vd.aggregator('sum', sum, 'sum of values')

By default, the sum function has the argument start=0.
This means that it only works to sum types which are compatible with integers.
For example, if you try to sum datedelta values, you get:

unsupported operand type(s) for +: 'int' and 'datedelta'

Would it make sense to automatically supply the type of the first value we are aggregating to sum to allow it to sum types which are not compatible with int?

Or is there something else we can add to the definition of datedelta to allow it to be summed with the default start=0?

visidata/visidata/type_date.py

Line 96 in 4ffacbb

class datedelta(datetime.timedelta):

[saulpw]

Sure, that makes sense to me! I committed the change and it seems to work. (This probably should have been an issue instead.)

[daviewales]

Thanks! I wasn't sure where it should live. I can see a 'Create issue from discussion' button in the right sidebar. Do you want me to click it?

[saulpw]

Nah, that's okay. Next time :)