bpo-38382: Document the early-out behavior for a zero (GH-17037)
diff --git a/Doc/library/statistics.rst b/Doc/library/statistics.rst
index a702b24..00c0b53 100644
--- a/Doc/library/statistics.rst
+++ b/Doc/library/statistics.rst
@@ -164,7 +164,8 @@
The harmonic mean, sometimes called the subcontrary mean, is the
reciprocal of the arithmetic :func:`mean` of the reciprocals of the
data. For example, the harmonic mean of three values *a*, *b* and *c*
- will be equivalent to ``3/(1/a + 1/b + 1/c)``.
+ will be equivalent to ``3/(1/a + 1/b + 1/c)``. If one of the values
+ is zero, the result will be zero.
The harmonic mean is a type of average, a measure of the central
location of the data. It is often appropriate when averaging
@@ -190,6 +191,10 @@
:exc:`StatisticsError` is raised if *data* is empty, or any element
is less than zero.
+ The current algorithm has an early-out when it encounters a zero
+ in the input. This means that the subsequent inputs are not tested
+ for validity. (This behavior may change in the future.)
+
.. versionadded:: 3.6