Why Doesn T 0.1 0.2 0.3 Equal 0.0 In Python

Python Programming

As a Python programmer, I have often encountered a puzzling phenomenon: why doesn’t 0.1 + 0.2 equal 0.3? At first glance, it seems like a simple arithmetic operation, but when I tried it in Python, I was surprised to find that the result was not what I expected.

Let’s dive deep into this issue and understand why Python behaves this way.

Understanding Floating-Point Numbers

In order to understand why 0.1 + 0.2 does not equal 0.3 in Python, we need to understand how floating-point numbers are represented and stored in a computer’s memory.

Floating-point numbers are approximations of real numbers. They are stored in binary format using a finite number of bits. This means that not all real numbers can be represented exactly in the computer’s memory. Instead, the computer approximates the number to the closest possible value that can be represented.

Rounding Errors

The reason why 0.1 + 0.2 does not equal 0.3 in Python is due to rounding errors that occur during the internal representation and arithmetic operations on floating-point numbers.

When we write 0.1 or 0.2 in Python, these numbers are internally stored as binary fractions that are close to, but not exactly equal to, their decimal representations. When we add these two numbers together, the result is a binary fraction that is also close to, but not exactly equal to, the decimal representation of 0.3.

Why Does This Happen?

This happens because decimal fractions, like 0.1 or 0.2, cannot be represented exactly in binary format. In base-10(decimal), we can represent 1/10 as 0.1. However, in base-2 (binary), 1/10 cannot be represented with a finite number of bits.

When we perform arithmetic operations on these binary approximations, small rounding errors accumulate and can lead to unexpected results. In the case of 0.1 + 0.2, the rounding errors add up and result in a number that is slightly different from 0.3.

Solutions and Workarounds

While it may seem frustrating to deal with these rounding errors, there are ways to mitigate the issue.

1. Using Decimal Module:

Python provides the decimal module, which allows us to perform decimal floating-point arithmetic with a higher precision. By using the Decimal class from this module, we can avoid the rounding errors and get the expected result.

2. Rounding the Result:

Another approach is to round the result of the arithmetic operation to a desired precision. This can be done using the built-in round() function or by formatting the result using string formatting options.

3. Using Fractions:

If precision is crucial and we want to avoid the rounding errors altogether, we can use the fractions module in Python. The Fraction class from this module allows us to perform arithmetic operations on rational numbers with arbitrary precision.


In conclusion, the reason why 0.1 + 0.2 does not equal 0.3 in Python is due to the inherent limitations of representing and performing arithmetic operations on floating-point numbers. These limitations are not unique to Python but are present in most programming languages.

While it may be frustrating at times, understanding how floating-point numbers work and utilizing the available tools and techniques can help us mitigate the impact of these rounding errors in our programs. So next time you encounter unexpected results in your Python code, keep in mind the quirks of floating-point arithmetic and explore the solutions mentioned above to achieve the desired precision.