Rounding edge cases for averages

[Douglas Cerna]

We use string formatting for printing averages:

"%.1f" % average

We store grades as decimals and in some cases this produces a rounding issue:

>>> average = Decimal('6.85')
>>> '%.1f' % average
'6.8'

We need to use decimal's rounding options for this.

This applies to the section gradebook as well as the report card.

[Gediminas Paulauskas (menesis)]

The problem is default decimal rounding setting of ROUND_HALF_EVEN (on 5 round to closest even number).

>>> print '{:.2}'.format(decimal.Decimal('6.75'))
6.8

>>> average = decimal.Decimal('6.85')

>>> print '{:.1f}'.format(average)
6.8

>>> ctx = decimal.Context(rounding=decimal.ROUND_HALF_UP)

>>> with decimal.localcontext(ctx):
    print '{:.1f}'.format(average)
...
6.9

Read https://docs.python.org/2/library/decimal.html