Prevent the random template filter from caching its output. Fixes #5678 (#7716)

homeassistant/helpers/template.py

@@ -2,9 +2,11 @@
 from datetime import datetime
 import json
 import logging
+import random
 import re
 
 import jinja2
+from jinja2 import contextfilter
 from jinja2.sandbox import ImmutableSandboxedEnvironment
 
 from homeassistant.const import (
@@ -418,6 +420,16 @@ def forgiving_float(value):
         return value
 
 
+@contextfilter
+def random_every_time(context, values):
+    """Choose a random value.
+
+    Unlike Jinja's random filter,
+    this is context-dependent to avoid caching the chosen value.
+    """
+    return random.choice(values)
+
+
 class TemplateEnvironment(ImmutableSandboxedEnvironment):
     """The Home Assistant template environment."""
 
@@ -435,6 +447,7 @@ ENV.filters['timestamp_utc'] = timestamp_utc
 ENV.filters['is_defined'] = fail_when_undefined
 ENV.filters['max'] = max
 ENV.filters['min'] = min
+ENV.filters['random'] = random_every_time
 ENV.globals['float'] = forgiving_float
 ENV.globals['now'] = dt_util.now
 ENV.globals['utcnow'] = dt_util.utcnow

tests/helpers/test_template.py

@@ -1,6 +1,7 @@
 """Test Home Assistant template helper methods."""
 from datetime import datetime
 import unittest
+import random
 from unittest.mock import patch
 
 from homeassistant.components import group
@@ -232,6 +233,15 @@ class TestHelpersTemplate(unittest.TestCase):
         self.assertEqual("1706951424.0",
                          template.Template(tpl, self.hass).render())
 
+    @patch.object(random, 'choice')
+    def test_random_every_time(self, test_choice):
+        """Ensure the random filter runs every time, not just once."""
+        tpl = template.Template('{{ [1,2] | random }}', self.hass)
+        test_choice.return_value = 'foo'
+        self.assertEqual('foo', tpl.render())
+        test_choice.return_value = 'bar'
+        self.assertEqual('bar', tpl.render())
+
     def test_passing_vars_as_keywords(self):
         """Test passing variables as keywords."""
         self.assertEqual(