Author WarrenWeckesser WarrenWeckesser 2019-10-06.01:46:18 -1.0 Yes <1570326378.93.0.0728676630318.issue38382@roundup.psfhosted.org>
Content
```The function statistics.harmonic_mean is supposed to raise a StatisticsError if any element in the input is negative.  It fails to do so if the negative element is preceded by a zero.  When there is a zero before the negative element, the function returns 0:

>>> from statistics import harmonic_mean
>>> harmonic_mean([0, -1, 3])
0

If the zero occurs after the negative value, the StatisticsError exception is correctly raised:

>>> harmonic_mean([-1, 0, 3])
Traceback (most recent call last):
File "<stdin>", line 1, in <module>
File "/Users/warren/repos/git/forks/cpython/Lib/statistics.py", line 406, in harmonic_mean
T, total, count = _sum(1/x for x in _fail_neg(data, errmsg))
File "/Users/warren/repos/git/forks/cpython/Lib/statistics.py", line 164, in _sum
for typ, values in groupby(data, type):
File "/Users/warren/repos/git/forks/cpython/Lib/statistics.py", line 406, in <genexpr>
T, total, count = _sum(1/x for x in _fail_neg(data, errmsg))
File "/Users/warren/repos/git/forks/cpython/Lib/statistics.py", line 289, in _fail_neg
raise StatisticsError(errmsg)
statistics.StatisticsError: harmonic mean does not support negative values
>>>

The problem is in this code in the function harmonic_mean:

try:
T, total, count = _sum(1/x for x in _fail_neg(data, errmsg))
except ZeroDivisionError:
return 0

When the zero occurs before the negative value, the ZeroDivisionError is raised before the negative value has been seen by the generator _fail_neg, and the function returns 0.```
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Date User Action Args
2019-10-06 01:46:18WarrenWeckessersetrecipients: + WarrenWeckesser
2019-10-06 01:46:18WarrenWeckessersetmessageid: <1570326378.93.0.0728676630318.issue38382@roundup.psfhosted.org>