Fmean

Fmean, commonly referred to as fmean, is a function in the Python statistics module that computes the arithmetic mean of a numeric data sequence. Introduced in Python 3.8, it provides a more numerically stable and often more accurate alternative to the straightforward sum(data) / n approach, especially for large or uneven data sets. The function is designed to reduce floating-point rounding errors by using a robust summation method during accumulation and subsequent division by the count of items.

Usage and behavior: fmean accepts any non-empty iterable of numbers and returns a float representing the arithmetic mean. If the input is empty, it raises a StatisticsError. If any element is non-numeric, a TypeError is raised. The function is intended for numeric data types such as int and float; in practice, elements should be real numbers. If the data contain special values like NaN or Inf, those values propagate through the calculation, and the result may be NaN or Inf accordingly.

Implementation and characteristics: fmean performs a single-pass computation using a numerically stable summation approach to mitigate precision loss that can occur with large sums. It does not require the input to be converted to a list first, making it suitable for streaming data or large datasets where memory efficiency matters. The result is always a float, aligning with Python’s general behavior for floating-point means.

Example: from statistics import fmean; fmean([1, 2, 3, 4]) returns 2.5. See also mean, fsum, and the statistics module for related numerical tools.