Avoid repeatedly appending to yaml_implicit_resolvers

psphicas · ingydotnet · commit fc914d52c43f · 2021-01-13T16:58:40.000-05:00
Repeated calls to `resolve` can experience performance degredation, if `add_implicit_resolver` has been called with `first=None` (to add an implicit resolver with an unspecified first character). For example, every time `foo` is encountered, the "wildcard implicit resolvers" (with `first=None`) will be appended to the list of implicit resolvers for strings starting with `f`, which will normally be the resolver for booleans. The list `yaml_implicit_resolvers['f']` will keep getting longer. The same behavior applies for any first-letter matches with existing implicit resolvers. This change avoids unintentionally mutating the lists in the class-level dict `yaml_implicit_resolvers` by looping through a temporary copy. Fixes: #439
diff --git a/lib/yaml/resolver.py b/lib/yaml/resolver.py
@@ -146,8 +146,8 @@ def resolve(self, kind, value, implicit):
                 resolvers = self.yaml_implicit_resolvers.get(u'', [])
             else:
                 resolvers = self.yaml_implicit_resolvers.get(value[0], [])
-            resolvers += self.yaml_implicit_resolvers.get(None, [])
-            for tag, regexp in resolvers:
+            wildcard_resolvers = self.yaml_implicit_resolvers.get(None, [])
+            for tag, regexp in resolvers + wildcard_resolvers:
                 if regexp.match(value):
                     return tag
             implicit = implicit[1]
diff --git a/lib3/yaml/resolver.py b/lib3/yaml/resolver.py
@@ -146,8 +146,8 @@ def resolve(self, kind, value, implicit):
                 resolvers = self.yaml_implicit_resolvers.get('', [])
             else:
                 resolvers = self.yaml_implicit_resolvers.get(value[0], [])
-            resolvers += self.yaml_implicit_resolvers.get(None, [])
-            for tag, regexp in resolvers:
+            wildcard_resolvers = self.yaml_implicit_resolvers.get(None, [])
+            for tag, regexp in resolvers + wildcard_resolvers:
                 if regexp.match(value):
                     return tag
             implicit = implicit[1]
