Change regex match() to search()

re.match() only matches from the beginning of the line, but sometimes
we have matchers that rely on the caret to differentiate between
the numerator and denominator.

This commit changes to re.search(), which does not start looking
at the beginning of the string.

backdrop/transformers/tasks/rate.py

@@ -23,7 +23,7 @@ def group_by(keys, arr):
 
 
 def pattern_filter(key, pattern, datum):
-    return key in datum and datum[key] and pattern.match(datum[key])
+    return key in datum and datum[key] and pattern.search(datum[key])
 
 
 def sum_matching(data, matchKey, pattern, valueKey):

tests/transformers/tasks/test_rate.py

@@ -9,36 +9,42 @@
         "_end_at": '2013-12-02T00:00:00+00:00',
         "_start_at": '2013-11-25T00:00:00+00:00',
         "eventCategory": 'start',
+        "channel": "non-digital",
         "uniqueEvents:sum": 15.0
     },
     {
         "_end_at": '2013-12-09T00:00:00+00:00',
         "_start_at": '2013-12-02T00:00:00+00:00',
         "eventCategory": 'start',
+        "channel": "non-digital",
         "uniqueEvents:sum": 25.0
     },
     {
         "_end_at": '2013-12-02T00:00:00+00:00',
         "_start_at": '2013-11-25T00:00:00+00:00',
         "eventCategory": 'confirm',
+        "channel": "digital",
         "uniqueEvents:sum": 8.0
     },
     {
         "_end_at": '2013-12-09T00:00:00+00:00',
         "_start_at": '2013-12-02T00:00:00+00:00',
         "eventCategory": 'confirm',
+        "channel": "digital",
         "uniqueEvents:sum": 12.0
     },
     {
         "_end_at": '2013-12-02T00:00:00+00:00',
         "_start_at": '2013-11-25T00:00:00+00:00',
         "eventCategory": 'done',
+        "channel": "another-channel",
         "uniqueEvents:sum": 10.0
     },
     {
         "_end_at": '2013-12-09T00:00:00+00:00',
         "_start_at": '2013-12-02T00:00:00+00:00',
         "eventCategory": 'done',
+        "channel": "another-channel",
         "uniqueEvents:sum": None
     }
 ]
@@ -68,3 +74,16 @@ def test_compute(self):
             is_('2013-12-02T00:00:00+00:00'))
         assert_that(transformed_data[0]['rate'], is_(2.0 / 3.0))
         assert_that(transformed_data[1]['rate'], is_(None))
+
+    def test_regex_matching_supports_carets(self):
+        # The numeratorMatcher should match just "digital"
+        # The denominatorMatcher should match both "digital" and "non-digital"
+        transformed_data = compute(data, {
+            "denominatorMatcher": 'digital$',
+            "numeratorMatcher": '^digital$',
+            "matchingAttribute": 'channel',
+            "valueAttribute": 'uniqueEvents:sum',
+        })
+
+        assert_that(transformed_data[0]['rate'], is_(8.0 / (8.0 + 15.0)))
+        assert_that(transformed_data[1]['rate'], is_(12.0 / (12.0 + 25.0)))