Why Does Python Return 3.3333333335 Not 3.33333

Python Programming

Have you ever wondered why Python sometimes returns long and seemingly imprecise decimal numbers instead of the rounded values you expect? As a Python enthusiast, I’ve encountered this question myself and today I’m going to dive deep into the details to help you understand why Python returns 3.3333333335 instead of 3.33333.

Python, like many other programming languages, uses floating-point arithmetic to perform calculations with decimal numbers. However, floating-point arithmetic has inherent limitations that can lead to small inaccuracies in the results.

When we write 3.33333 in Python, we are using a decimal representation with limited precision. The actual value of 3.33333 cannot be precisely represented using the finite number of bits available in the computer’s memory. Therefore, Python approximates the value as closely as possible but doesn’t guarantee an exact representation.

Python uses the IEEE 754 standard for floating-point arithmetic, which stores floating-point numbers using a combination of sign, exponent, and fraction bits. These bits have limited precision, typically 32 or 64 bits, depending on the underlying hardware. In this case, Python uses double precision, which means it uses 64 bits to represent floating-point numbers.

When we perform calculations in Python, the limited precision of floating-point numbers can lead to small rounding errors. These errors accumulate during arithmetic operations and can result in slightly different values than we expect.

In the case of 3.33333, Python approximates the value as 3.3333333333333335 because the actual value is slightly larger than 3.33333 due to the rounding error. While this difference may seem insignificant, it is a consequence of the limitations of floating-point arithmetic.

It’s important to note that Python provides various techniques and libraries for handling decimal arithmetic with arbitrary precision, such as the decimal module. If you require precise decimal calculations, using the decimal module can help avoid the rounding errors associated with floating-point arithmetic.

To summarize, Python returns 3.3333333335 instead of 3.33333 because of the limitations of floating-point arithmetic and the finite precision of floating-point numbers. These rounding errors are inherent to the way computers represent and manipulate decimal numbers using binary digits.


Understanding why Python returns 3.3333333335 instead of 3.33333 requires delving into the intricacies of floating-point arithmetic and the limitations of representing decimal numbers in binary form. While these rounding errors may seem minor, they highlight the importance of being aware of the limitations of floating-point arithmetic and considering alternative approaches, such as the decimal module, when precise decimal calculations are required.