Issue 13355: Make random.triangular degrade gracefully when low == high.

Lib/random.py

@@ -355,7 +355,10 @@ class Random(_random.Random):
 
         """
         u = self.random()
-        c = 0.5 if mode is None else (mode - low) / (high - low)
+        try:
+            c = 0.5 if mode is None else (mode - low) / (high - low)
+        except ZeroDivisionError:
+            return low
         if u > c:
             u = 1.0 - u
             c = 1.0 - c

Lib/test/test_random.py

@@ -602,7 +602,7 @@ class TestDistributions(unittest.TestCase):
         for variate, args, expected in [
                 (g.uniform, (10.0, 10.0), 10.0),
                 (g.triangular, (10.0, 10.0), 10.0),
-                #(g.triangular, (10.0, 10.0, 10.0), 10.0),
+                (g.triangular, (10.0, 10.0, 10.0), 10.0),
                 (g.expovariate, (float('inf'),), 0.0),
                 (g.vonmisesvariate, (3.0, float('inf')), 3.0),
                 (g.gauss, (10.0, 0.0), 10.0),

Misc/NEWS

@@ -24,6 +24,9 @@ Library
 - Issue #14710: pkgutil.find_loader() no longer raises an exception when a
   module doesn't exist.
 
+- Issue #13355: random.triangular() no longer fails with a ZeroDivisionError
+  when low equals high.
+
 - Issue #21538: The plistlib module now supports loading of binary plist files
   when reference or offset size is not a power of two.