Python round() Function Tutorial (With Examples)

In Python, the round() function is a built-in function that allows you to round a given number to a specified number of decimal places. Rounding numbers is a common operation in various mathematical and scientific computations, as well as in everyday programming tasks. In this tutorial, we will explore the usage of the round() function with detailed explanations and practical examples to help you understand how to effectively use it in your code.

Table of Contents

1. Introduction to the round() Function
2. Syntax of the round() Function
3. Rounding to a Specified Number of Decimal Places

• Example 1: Basic Usage
• Example 2: Rounding Floating-Point Numbers

1. Rounding to the Nearest Integer

• Example 3: Rounding Positive and Negative Numbers

1. Rounding to a Specified Significant Figure

• Example 4: Rounding with Significant Figures

1. Handling Edge Cases and Special Considerations
2. Conclusion

1. Introduction to the round() Function

The round() function is used to round a given number to the nearest value according to a specified precision. Precision can refer to the number of decimal places or significant figures to which the number should be rounded. This function can be particularly useful when dealing with calculations that require a specific level of accuracy.

2. Syntax of the round() Function

The syntax of the round() function is as follows:

round(number, ndigits)

• number: This is the number that you want to round.
• ndigits: This is the number of decimal places to which you want to round the number.

3. Rounding to a Specified Number of Decimal Places

Example 1: Basic Usage

Let’s start with a simple example to illustrate how the round() function works:

# Rounding to 2 decimal places
num1 = 3.14159
rounded_num1 = round(num1, 2)
print(rounded_num1)  # Output: 3.14

In this example, we have a floating-point number num1 with the value 3.14159. By calling round(num1, 2), we round num1 to two decimal places, resulting in the value 3.14.

Example 2: Rounding Floating-Point Numbers

# Rounding positive and negative floating-point numbers
num2 = 5.6789
num3 = -2.3456

rounded_num2 = round(num2, 2)
rounded_num3 = round(num3, 2)

print(rounded_num2)  # Output: 5.68
print(rounded_num3)  # Output: -2.35

In this example, we have both positive and negative floating-point numbers. By rounding num2 and num3 to two decimal places, we get 5.68 and -2.35, respectively.

4. Rounding to the Nearest Integer

The round() function can also be used to round a number to the nearest integer when the ndigits argument is set to 0.

Example 3: Rounding Positive and Negative Numbers

# Rounding positive and negative numbers to the nearest integer
num4 = 8.6
num5 = -7.3

rounded_num4 = round(num4)
rounded_num5 = round(num5)

print(rounded_num4)  # Output: 9
print(rounded_num5)  # Output: -7

In this example, we are rounding num4 to the nearest integer, resulting in 9, and rounding num5 to the nearest integer, resulting in -7.

5. Rounding to a Specified Significant Figure

Apart from rounding to a specific number of decimal places, the round() function can be used to round a number to a specified number of significant figures. This can be useful when you want to ensure a certain level of precision in your calculations.

Example 4: Rounding with Significant Figures

# Rounding to a specified number of significant figures
num6 = 12345.6789

rounded_num6_3sf = round(num6, 3)
rounded_num6_5sf = round(num6, 5)

print(rounded_num6_3sf)  # Output: 12300.0
print(rounded_num6_5sf)  # Output: 12345.0

In this example, we have the number num6 with a value of 12345.6789. By rounding it to three significant figures, we get 12300.0, and by rounding it to five significant figures, we get 12345.0.

6. Handling Edge Cases and Special Considerations

It’s important to note that the round() function uses the “round half to even” strategy for rounding numbers. This means that if a number is exactly halfway between two rounded values, it will round to the nearest even number. For example:

num7 = 2.5
num8 = 3.5

rounded_num7 = round(num7)
rounded_num8 = round(num8)

print(rounded_num7)  # Output: 2
print(rounded_num8)  # Output: 4

In this case, 2.5 rounds to 2 because it’s exactly halfway between 2 and 3, and 3.5 rounds to 4 for the same reason.

7. Conclusion

The round() function in Python is a versatile tool for rounding numbers to a specified number of decimal places or significant figures. It’s useful in a wide range of applications, from financial calculations to scientific computations. By understanding the syntax and various examples provided in this tutorial, you should now have a solid grasp of how to use the round() function effectively in your Python programs. Remember to consider special cases and choose the appropriate rounding strategy based on the requirements of your specific task. Happy coding!