Issue #4869: clarify documentation for random.expovariate.
diff --git a/Doc/library/random.rst b/Doc/library/random.rst
index 858888c..63c4bc7 100644
--- a/Doc/library/random.rst
+++ b/Doc/library/random.rst
@@ -210,9 +210,11 @@
.. function:: expovariate(lambd)
- Exponential distribution. *lambd* is 1.0 divided by the desired mean. (The
- parameter would be called "lambda", but that is a reserved word in Python.)
- Returned values range from 0 to positive infinity.
+ Exponential distribution. *lambd* is 1.0 divided by the desired
+ mean. It should be nonzero. (The parameter would be called
+ "lambda", but that is a reserved word in Python.) Returned values
+ range from 0 to positive infinity if *lambd* is positive, and from
+ negative infinity to 0 if *lambd* is negative.
.. function:: gammavariate(alpha, beta)
diff --git a/Lib/random.py b/Lib/random.py
index 5879340..8b4c38e 100644
--- a/Lib/random.py
+++ b/Lib/random.py
@@ -413,9 +413,11 @@
def expovariate(self, lambd):
"""Exponential distribution.
- lambd is 1.0 divided by the desired mean. (The parameter would be
- called "lambda", but that is a reserved word in Python.) Returned
- values range from 0 to positive infinity.
+ lambd is 1.0 divided by the desired mean. It should be
+ nonzero. (The parameter would be called "lambda", but that is
+ a reserved word in Python.) Returned values range from 0 to
+ positive infinity if lambd is positive, and from negative
+ infinity to 0 if lambd is negative.
"""
# lambd: rate lambd = 1/mean