How can I format a decimal to always show 2 decimal places?

python

decimal

formatting

rounding

byAlex Kataev·Sep 26, 2024

When you need quick and precise string formatting to two decimal places, Python's format() function and f-strings with :.2f specifier are your go-to tools:

# Bruce Wayne's bank balance probably!
number = 123.456
formatted_number = f"{number:.2f}"
print(formatted_number)  # Batman's bank says: "123.46"

These methods ensure your number is elegantly dressed in a string, showing off its suave two digits after the decimal.

Optimal tools for finance

Are you handling money, they say it's a rich man's world? For rendering financial amounts accurately, Python's Decimal module behaves like the honest banker you always needed:

from decimal import Decimal

amount = Decimal('123.456')
formatted_amount = f"{amount:.2f}"
print(formatted_amount)  # Your banker approves: "123.46"

If you're squaring off against the Joker's financial crimes and need round amounts to the nearest cent, use quantize() for reliable backup:

from decimal import Decimal, ROUND_HALF_UP

money = Decimal('123.456') # Bruce Wayne's loose change
rounded_money = money.quantize(Decimal('0.01'), rounding=ROUND_HALF_UP)
print(f"{rounded_money:.2f}")  # Alfred makes sure you see "123.46"

Data clarity

Formatting is to data what Batsuit is to Batman - it asserts identity and clarity. When faced with a crowd of numbers, ensure there is order:

numbers = [123.456, 123, 123.5]  # Even Batman has a list of numbers

formatted_numbers = [f"{x:.2f}" for x in numbers]
for n in formatted_numbers:
    print(n)  # Gotham PD now reads this easily

123.46
123.00
123.50

Navigating old and new roads in code

In your adventures with legacy code, you'll probably stumble upon % formatting. Here's how you navigate this alongside the .format() method:

# Old-style % formatting, like Grayson's dance moves
print("%.2f" % 123.456)  # Robin says: "123.46"

# New-style .format() formatting, Batman’s groovy counterpart
print("{:.2f}".format(123.456))  # Batmobile displays: "123.46"

Unraveling the mystery of rounding

The round() function is commonly used but it's more unpredictable than the Riddler on weekends:

# To two decimal places, Gordon! Always two decimal places!
rounded_num = round(2.5, 2) 
print(f"{rounded_num:.2f}")  # "2.50"

But be warned, Bat-friends! Using only round() can lead to unexpected results:

print(round(2.675, 2))  # You might expect 2.68, but you get 2.67!

Using Decimal is a safe path through this Gotham-esque chaos.

Complex architectures of knowledge

Grasping the finer intricacies of formatting requires a detour through the Python documentation. At Pyformat.info, you can see format-manipulating marvels that would stun even the Joker.