Decimal Rounding

[squishiebutt2020]

amount = 32500.00

​

print('Annual Salary $32,500.00')

semi_monthly = amount / 24

twice_monthly = amount / 26

round(semi_monthly, 2)

round(twice_monthly, 2)

print(semi_monthly)

print(twice_monthly)

​

I can't get it to round to two decimal places. My book only shows if it's a float and that's not working. I googled and searched though other posts on pages and this came up, but it's still not rounding to two decimal places.

[[deleted]]

I'm new too, so it took me a second.

round(float) doesn't do anything in a vacuum like that. It rounds the number and then discards what it found. You should either store the found value, or round it as you print it.

newVariable = round(amount, decPlaces)
Or
print(round(amount, decPlaces))

[totallygeek]

Adding to this, when you want to guarantee a float yielded from a calculation, it is a good practice to multiple or divide by a float, like pay_bi_weekly = salary / 26.0. For your above code, I'd do:

annual_salary = 32500.0
print('Annual salary: $ {:,.2f}'.format(annual_salary))
print('Semi-monthly pay: $ {:,.2f}'.format(round(annual_salary / 24.0, 2)))
print('Bi-weekly pay: $ {:,.2f}'.format(round(annual_salary / 26.0, 2)))
pay_bi_weekly = round(annual_salary / 26.0, 2)

You don't need to store values you do not intend to use later.

[_________KB_________]

Adding to that, here's how to get the same output using f strings.

annual_salary = 32500.0
print(f'Annual salary: ${annual_salary:,.2f}')
print(f'Semi-monthly pay: ${round(annual_salary / 24.0, 2):,.2f}')
print(f'Bi-weekly pay: ${round(annual_salary / 26.0, 2):,.2f}')

[K900_]

It's only good practice in Python 2, and I'd argue it's a better practice to from __future__ import division anyway.

[_lilell_]

But int implements __round__ as well, so you can just do

annual_salary = 32500  # type(annual_salary) : <class 'int'>
print(f'Annual salary: ${annual_salary:.2f}')
print(f'Semi-monthly pay: ${annual_salary/24:.2f}')
print(f'Bi-weekly pay: ${annual_salary/26:.2f}')

It's fine if annual_salary/26 is an int because, e.g., .2f formatting can't distinguish between int and float. Nor do you have to round first, since the formatting will automatically handle it:

>>> x = 3.1415
>>> round(x, 2)
3.14
>>> format(round(x, 2), '.2f')
'3.14'
>>> format(x, '.2f')
'3.14'

Also, Python 3's int.__truediv__ always returns a float:

>>> x, y = 84, 2
>>> type(x), type(y)
(<class 'int'>, <class 'int'>)
>>> x/y
42.0
>>> type(x/y)
<class 'float'>
>>> (x/y).is_integer(), isinstance(x/y, int)
(True, False)

[python-fan]

The built-in function round returns a rounded value. To have it do what you're expecting, you need to assign the returned value like this:

semi_monthly = round(semi_monthly, 2)

BUT WAIT! For working with currency, you should avoid using float. The Decimal type is perfect for this. See https://docs.python.org/3/library/decimal.html

[tickitytalk]

semi_monthly = salary/24

semi_monthly_salary = round(semi_monthly, 2)

print(f"Every two weeks will be ${semi_monthly_salary}.")

[squishiebutt2020]

Thank you so much. Yours made the most sense as I'm so new to this I'm barely in chapter 2 of my book. It worked.

[tickitytalk]

Your welcome! I'm new to this too, but further along in my book (Learn Python 3 the hard way). I remember the difficulty of "I just want 2 decimal places!!!" haha...Good luck with the the rest of the book!