Make percentage_format_string support str.format() syntax

CHANGELOG.md

@@ -22,6 +22,7 @@
 - Apply percentage_format_string to match_body percentage value; will appear in new percentage_formatted key - [#387](https://github.com/jertel/elastalert2/pull/387) - @iamxeph
 - Add support for Kibana 7.14 for Kibana Discover - [#392](https://github.com/jertel/elastalert2/pull/392) - @nsano-rururu
 - Add metric_format_string optional configuration for Metric Aggregation to format aggregated value - [#399](https://github.com/jertel/elastalert2/pull/399) - @iamxeph
+- Make percentage_format_string support format() syntax in addition to old %-formatted syntax - [#403](https://github.com/jertel/elastalert2/pull/403) - @iamxeph
 
 ## Other changes
 - [Tests] Improve test code coverage - [#331](https://github.com/jertel/elastalert2/pull/331) - @nsano-rururu

docs/source/ruletypes.rst

@@ -1347,8 +1347,7 @@ evaluated separately against the threshold(s).
 
 ``sync_bucket_interval``: See ``sync_bucket_interval`` in  Metric Aggregation rule
 
-``percentage_format_string``: An optional format string to apply to the percentage value in the alert match text. This also adds 'percentage_formatted' value to the match_body in addition to raw, unformatted 'percentage' value so that you can use the formatted value for ``alert_subject_args`` and ``alert_text_args``. Must be a valid python format string.
-For example, "%.2f" will round it to 2 decimal places.
+``percentage_format_string``: An optional format string applies to the percentage value in the alert match text and match_body. This adds 'percentage_formatted' value to the match_body in addition to raw, unformatted 'percentage' value so that you can use the values for ``alert_subject_args`` and ``alert_text_args``. Must be a valid python format string. Both format() and %-formatted syntax works. For example, both "{:.2f}" and "%.2f" will format '96.6666667' to '96.67'.
 See: https://docs.python.org/3.4/library/string.html#format-specification-mini-language
 
 ``min_denominator``: Minimum number of documents on which percentage calculation will apply. Default is 0.

elastalert/ruletypes.py

@@ -1258,7 +1258,7 @@ def __init__(self, *args):
     def get_match_str(self, match):
         percentage_format_string = self.rules.get('percentage_format_string', None)
         message = 'Percentage violation, value: %s (min: %s max : %s) of %s items\n\n' % (
-            percentage_format_string % (match['percentage']) if percentage_format_string else match['percentage'],
+            self.format_string(percentage_format_string, match['percentage']) if percentage_format_string else match['percentage'],
             self.rules.get('min_percentage'),
             self.rules.get('max_percentage'),
             match['denominator']
@@ -1297,7 +1297,7 @@ def check_matches(self, timestamp, query_key, aggregation_data):
                     match = {self.rules['timestamp_field']: timestamp, 'percentage': match_percentage, 'denominator': total_count}
                     percentage_format_string = self.rules.get('percentage_format_string', None)
                     if percentage_format_string is not None:
-                        match['percentage_formatted'] = percentage_format_string % (match_percentage)
+                        match['percentage_formatted'] = self.format_string(percentage_format_string, match_percentage)
                     if query_key is not None:
                         match = expand_string_into_dict(match, self.rules['query_key'], query_key)
                     self.add_match(match)
@@ -1308,3 +1308,9 @@ def percentage_violation(self, match_percentage):
         if 'min_percentage' in self.rules and match_percentage < self.rules['min_percentage']:
             return True
         return False
+
+    def format_string(self, format_config, target_value):
+        if (format_config.startswith('{')):
+            return format_config.format(target_value)
+        else:
+            return format_config % (target_value)

tests/rules_test.py

@@ -1303,6 +1303,12 @@ def test_percentage_match():
     assert '76.1589403974' in rule.get_match_str(rule.matches[0])
     assert rule.matches[0]['percentage'] == 76.15894039742994
     assert 'percentage_formatted' not in rule.matches[0]
+    rules['percentage_format_string'] = '{:.2f}'
+    rule = PercentageMatchRule(rules)
+    rule.check_matches(datetime.datetime.now(), None, create_percentage_match_agg(76.666666667, 24))
+    assert '76.16' in rule.get_match_str(rule.matches[0])
+    assert rule.matches[0]['percentage'] == 76.15894039742994
+    assert rule.matches[0]['percentage_formatted'] == '76.16'
     rules['percentage_format_string'] = '%.2f'
     rule = PercentageMatchRule(rules)
     rule.check_matches(datetime.datetime.now(), None, create_percentage_match_agg(76.666666667, 24))