How to Round to 2 Decimal Places in Python

Have you ever found yourself in a situation where you have to round off a number to two decimal places in your Python program? Rounding off to two decimal places is a common task in data science, finance, and other fields that deal with numerical data. It involves converting a number to the nearest value with two decimal places. In this article, we will explore how to round to two decimal places in Python, with examples of different scenarios where this may be necessary.

Understanding the Basics of Rounding in Python

Before we dive into the specifics of how to round to two decimal places, it is essential to have a basic understanding of rounding in Python. Rounding is a mathematical function that converts a value to the nearest whole number or a specified number of decimal places. Python has built-in functions for rounding, which makes it easy to perform this operation on numerical data.

Python provides two built-in functions for rounding: round() and format(). These functions offer different ways of rounding numbers, depending on the specific needs of your program. The round() function rounds a number to the nearest whole number or a specified number of decimal places. The format() function formats a number to a specified number of decimal places, without rounding it off. In this article, we will focus on the round() function, which is the most commonly used function for rounding in Python.

Rounding to Two Decimal Places in Python Using the Round() Function

The round() function in Python takes two parameters: the number to be rounded, and the number of decimal places to round to. If the number of decimal places is not specified, the function rounds the number to the nearest whole number. To round to two decimal places, we need to specify the second parameter as 2. Here is an example:

num = 3.14159
rounded_num = round(num, 2)
print(rounded_num)

In the code above, we define a variable num as 3.14159. We then use the round() function to round off num to two decimal places, and store the result in a new variable rounded_num. Finally, we print the rounded number using the print() function. The output of this code will be:

3.14

As you can see, the round() function has rounded off the number to two decimal places, giving us 3.14.

Rounding Negative Numbers in Python

When rounding negative numbers in Python, it is essential to understand how the round() function works. By default, the function rounds to the nearest even number when the number being rounded is equidistant from two possible values. This is called "bankers’ rounding" or "round-to-even." For example:

num = -1.5
rounded_num = round(num)
print(rounded_num)

In the code above, we define a variable num as -1.5. We then use the round() function to round off num to the nearest whole number, and store the result in a new variable rounded_num. Finally, we print the rounded number using the print() function. The output of this code will be:

-2

As you can see, the round() function has rounded off the number to the nearest even number, which is -2. If we want to round off negative numbers to two decimal places, we need to specify the second parameter of the round() function as -2. For example:

num = -3.14159
rounded_num = round(num, 2)
print(rounded_num)

In the code above, we define a variable num as -3.14159. We then use the round() function to round off num to two decimal places, and store the result in a new variable rounded_num. Finally, we print the rounded number using the print() function. The output of this code will be:

-3.14

As you can see, the round() function has rounded off the number to two decimal places, giving us -3.14.

Rounding Large Numbers in Python

When dealing with large numbers in Python, rounding to two decimal places may result in a number that is still too large to be displayed on the screen. In such cases, we can use the format() function to format the number to two decimal places, without rounding it off. Here is an example:

num = 123456789.123456789
formatted_num = '{:.2f}'.format(num)
print(formatted_num)

In the code above, we define a variable num as 123456789.123456789. We then use the format() function to format num to two decimal places, and store the result in a new variable formatted_num. Finally, we print the formatted number using the print() function. The output of this code will be:

123456789.12

As you can see, the format() function has formatted the number to two decimal places, without rounding it off.

Rounding Numbers in Data Science

Rounding off numbers is a common task in data science, where we may be dealing with large datasets containing numerical values. In such cases, we may need to round off numbers to two decimal places for analysis or visualization purposes. For example, we may want to round off a list of prices to two decimal places before plotting them on a graph. Here is an example:

prices = [2.345, 3.456, 4.567, 5.678, 6.789]
rounded_prices = [round(price, 2) for price in prices]
print(rounded_prices)

In the code above, we define a list of prices as prices. We then use a list comprehension to round off each price in the list to two decimal places, and store the result in a new list rounded_prices. Finally, we print the rounded prices using the print() function. The output of this code will be:

[2.35, 3.46, 4.57, 5.68, 6.79]

As you can see, each price in the list has been rounded off to two decimal places, giving us a list of rounded prices that can be used for analysis or visualization.

Rounding Numbers in Financial Calculations

Rounding off numbers is also a common task in finance, where we may be dealing with monetary values that need to be rounded off to two decimal places. For example, we may want to calculate the total cost of an order, including taxes and shipping, and round off the final value to two decimal places. Here is an example:

subtotal = 56.78
tax = 0.06
shipping = 10.00
total = round(subtotal * (1 + tax) + shipping, 2)
print(total)

In the code above, we define a subtotal as 56.78, a tax rate as 0.06, and a shipping cost as 10.00. We then calculate the total cost of the order, including taxes and shipping, by multiplying the subtotal by the tax rate, adding the shipping cost, and rounding off the final value to two decimal places using the round() function. Finally, we print the total cost using the print() function. The output of this code will be:

68.11

As you can see, the total cost has been rounded off to two decimal places, giving us a final value that can be used for financial calculations.

Final Thoughts

Rounding off numbers to two decimal places is a common task in Python programming, especially in data science and finance. Python provides the round() function, which makes it easy to perform this operation on numerical data. By understanding the basics of rounding in Python and the different scenarios where rounding may be necessary, you can write more efficient and accurate Python programs that deal with numerical data.

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