dec.py

from decimal import *

PLACES = Decimal(10) ** -6

option1 =  Decimal("1000.1111")
option2 = Decimal("300.2222")
option3 = Decimal("500.3333")

total = option1 - option2 - option3


print(total)
# output 199.5556

new_option = Decimal("100")
total = total + new_option
print(total)
print("----------------")

ctx = getcontext()
ctx.rounding = ROUND_HALF_UP


print(total.quantize(PLACES))