Round an answer to 2 decimal places in Python

Question

The issue i am having is my rounding my results to 2 decimal places. My app gets the right results, however, i am having difficulty making the app round to the nearest decimal as you would with currency

cost = input("\nEnter the 12 month cost of the Order: ")
cost = float(cost)

print("\n12 Month Cost:",
  cost * 1,"USD")
print("6 Month Cost:",
  cost * 0.60,"USD")
print("3 Month Cost:",
  cost * 0.36,"USD")

so for example if the 12 month price is $23, the 6 month price is 13.799999999999999 but i want it to show 13.80

I've looked around google and how to round a number but couldn't find much help on rounding a result.

Answer 1

You should use a format specifier:

print("6 Month Cost: %.2fUSD" % (cost * .6))

Even better, you shouldn't rely on floating point numbers at all and use the decimal module instead, which gives you arbitrary precision and much more control over the rounding method:

from decimal import Decimal, ROUND_HALF_UP
def round_decimal(x):
  return x.quantize(Decimal(".01"), rounding=ROUND_HALF_UP)

cost = Decimal(input("Enter 12 month cost: "))
print("6 Month Cost: ", round_decimal(cost * Decimal(".6")))

Answer 2

If you just want to have it as a string, format can help:

format(cost, '.2f')

This function returns a string that is formated as defined in the second parameter. So if cost contains 3.1418 the code above returns the string '3.14'.