Issue #13355: Raise ValueError on random.triangular call with invalid params.
Initial patch by Yuriy Senko.
diff --git a/Lib/random.py b/Lib/random.py
index af04ab2..8560fb9 100644
--- a/Lib/random.py
+++ b/Lib/random.py
@@ -367,6 +367,16 @@
http://en.wikipedia.org/wiki/Triangular_distribution
"""
+ # Sanity check. According to the doc low must be less or equal to
+ # high. And mode should be somewhere between these bounds.
+ if low > high:
+ raise ValueError('high cannot be less then low.')
+ if mode is not None and (mode < low or mode > high):
+ raise ValueError('mode must be between low and high.')
+
+ if high == low:
+ return low
+
u = self.random()
c = 0.5 if mode is None else (mode - low) / (high - low)
if u > c: