Python's round() Function: Banker's Rounding Explained

Did you know? Python’s round() doesn’t always round .5 upward. Most people expect: 2.5 → 3 3.5 → 4 But in Python, this happens: Python round(2.5) # 2 round(3.5) # 4 round(4.5) # 4 round(5.5) # 6 Why does this happen? Python follows Banker’s Rounding, also called “round half to even.” When a number is exactly halfway between two integers, Python rounds it to the nearest even number, not always up. Why is this important? ✔ Reduces cumulative rounding bias ✔ More accurate for financial and statistical calculations ✔ Widely used in data science and scientific computing Key takeaway If you need traditional rounding (always round .5 up), you should use: math.floor(x + 0.5) or the decimal module with ROUND_HALF_UP Understanding small details like this makes you a better Python developer. #Python #Programming #DataScience #MachineLearning #CodingTips #PythonTricks

  • How Python Round Function Works

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