Add type-hints to yaml.py

sexpr/yaml.py

@@ -1,21 +1,26 @@
 import re
+from typing import TYPE_CHECKING, Match, Optional
 
 import yaml
 
+if TYPE_CHECKING:
+    from yamlloader.ordereddict.loaders import Loader
+    from yaml.nodes import ScalarNode
+
 
 class Regexpr(yaml.YAMLObject):
     yaml_tag = u'!regexpr'
 
-    def __init__(self, pattern):
-        self.pattern = pattern
-        self.re_pattern = re.compile(pattern)
-
-    def matches(self, string):
-        return self.re_pattern.match(string)
-
     @classmethod
-    def from_yaml(cls, loader, node):
+    def from_yaml(cls, loader: 'Loader', node: 'ScalarNode') -> 'Regexpr':
         return Regexpr(node.value)
 
+    def __init__(self, pattern: str) -> None:
+        self.pattern = pattern
+        self.re_pattern = re.compile(pattern)
+
     def __repr__(self):
         return '(regex %s)' % self.pattern
+
+    def matches(self, string: str) -> Optional[Match[str]]:
+        return self.re_pattern.match(string)