How To Round In Python

Python Programming

I’ve been coding in Python for quite some time now, and one of the things I find myself doing frequently is rounding numbers. Whether it’s for mathematical calculations or displaying data in a user-friendly format, rounding is a handy tool to have in your coding toolbox.

Understanding Python’s Built-in round() Function

Python provides a built-in function called round() that allows you to round a number to a specified number of digits. The basic syntax of the round() function is:

rounded_number = round(number, digits)

The number parameter is the number you want to round, and the digits parameter is the number of decimal places you want to round to. If the digits parameter is omitted, the round() function will round to the nearest whole number.

Let’s take a look at a few examples to see how the round() function works:

num1 = 3.14159
rounded_num1 = round(num1)
print(rounded_num1)  # Output: 3

num2 = 3.14159
rounded_num2 = round(num2, 2)
print(rounded_num2)  # Output: 3.14

num3 = 3.14159
rounded_num3 = round(num3, 4)
print(rounded_num3)  # Output: 3.1416

As you can see from the examples above, the round() function works as expected. It rounds the given number to the specified number of digits.

Handling Ties: Round Half to Even

When rounding numbers, it’s important to understand how ties are handled. In Python, the default behavior is to use the “Round Half to Even” strategy, also known as “Bankers’ rounding.”

In this strategy, if the number to be rounded is exactly halfway between two possible rounded values, the number is rounded to the nearest even number. This approach ensures that rounding is statistically fair and reduces bias.

Let’s look at an example to understand this:

num4 = 2.5
rounded_num4 = round(num4)
print(rounded_num4)  # Output: 2

num5 = 3.5
rounded_num5 = round(num5)
print(rounded_num5)  # Output: 4

In both cases, the numbers 2.5 and 3.5 are exactly halfway between two possible rounded values. According to the “Round Half to Even” strategy, they are rounded to the nearest even number (2 and 4, respectively).

Handling Negative Numbers

Now, what about rounding negative numbers? How does Python’s round() function handle them?

In Python, rounding negative numbers works slightly differently. The round() function rounds towards the nearest even integer, just like positive numbers.

Let’s see an example to understand this:

num6 = -3.5
rounded_num6 = round(num6)
print(rounded_num6)  # Output: -4

num7 = -2.5
rounded_num7 = round(num7)
print(rounded_num7)  # Output: -2

As you can see, the negative numbers -3.5 and -2.5 are rounded to the nearest even numbers (-4 and -2, respectively).

Conclusion

Rounding numbers in Python is a straightforward process using the built-in round() function. By understanding the basic syntax and how ties are handled, you can confidently round numbers to the desired precision in your coding projects. Just remember, when in doubt, Python uses the “Round Half to Even” strategy, ensuring unbiased and statistically fair rounding.