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Avoid repeatedly appending to yaml_implicit_resolvers
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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
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psphicas authored and ingydotnet committed Jan 13, 2021
1 parent a001f27 commit fc914d5
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Showing 2 changed files with 4 additions and 4 deletions.
4 changes: 2 additions & 2 deletions lib/yaml/resolver.py
Original file line number Diff line number Diff line change
Expand Up @@ -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]
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4 changes: 2 additions & 2 deletions lib3/yaml/resolver.py
Original file line number Diff line number Diff line change
Expand Up @@ -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]
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