python / python/cpython

statistics.fmean() does not support Decimal data, contrary to documentation

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#131,723 3 comments 0 reactions 1 assignee View on GitHub

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Since Mar 25, 2025.

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Description

Bug report

Bug description:

From manpage:
"Unless explicitly noted, these functions support int, float, Decimal and Fraction." and (for fmean)
"Convert data to floats and compute the arithmetic mean."

However:

Python 3.12.3 (main, Feb  4 2025, 14:48:35) [GCC 13.3.0] on linux
Type "help", "copyright", "credits" or "license" for more information.
>>> import statistics
>>> grades = [85, 92, 83, 91]
>>> weights = [0.20, 0.20, 0.30, 0.30]
>>> statistics.fmean(grades, weights)
87.6
>>> from decimal import Decimal
>>> grades = [Decimal("85"), Decimal("92"), Decimal("83"), Decimal("91")]
>>> statistics.fmean(grades, weights)
Traceback (most recent call last):
  File "<stdin>", line 1, in <module>
  File "/usr/lib/python3.12/statistics.py", line 517, in fmean
    num = sumprod(data, weights)
          ^^^^^^^^^^^^^^^^^^^^^^
TypeError: unsupported operand type(s) for *: 'decimal.Decimal' and 'float'

Contrary to documentation, statistics.fmean() does not convert data to floats.

CPython versions tested on:

3.12

Operating systems tested on:

Linux

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