Fix HeaderDict lint

qutebrowser/config/configtypes.py

@@ -1428,6 +1428,27 @@ class HeaderDict(BaseType):
 
     """A JSON-like dictionary for custom HTTP headers."""
 
+    def _validate_str(self, value, what):
+        """Check if the given thing is an ascii-only string.
+
+        Raises ValidationError if not.
+
+        Args:
+            value: The value to check.
+            what: Either 'key' or 'value'.
+        """
+        if not isinstance(value, str):
+            msg = "Expected string for {} {!r} but got {}".format(
+                what, value, type(value))
+            raise configexc.ValidationError(value, msg)
+
+        try:
+            value.encode('ascii')
+        except UnicodeEncodeError as e:
+            msg = "{} {!r} contains non-ascii characters: {}".format(
+                what.capitalize(), value, e)
+            raise configexc.ValidationError(value, msg)
+
     def validate(self, value):
         self._basic_validation(value)
         if not value:
@@ -1441,7 +1462,6 @@ class HeaderDict(BaseType):
         if not isinstance(json_val, dict):
             raise configexc.ValidationError(value, "Expected json dict, but "
                                             "got {}".format(type(json_val)))
-
         if not json_val:
             if self.none_ok:
                 return
@@ -1449,30 +1469,8 @@ class HeaderDict(BaseType):
                 raise configexc.ValidationError(value, "may not be empty!")
 
         for key, val in json_val.items():
-            if not isinstance(key, str):
-                msg = "Expected string for key {!r} but got {}".format(
-                    key, type(key))
-                raise configexc.ValidationError(value, msg)
-
-            if not isinstance(val, str):
-                msg = "Expected string for value {!r} but got {}".format(
-                    key, type(key))
-                raise configexc.ValidationError(value, msg)
-
-            try:
-                key.encode('ascii')
-            except UnicodeEncodeError as e:
-                msg = "Key {!r} contains non-ascii characters: {}".format(
-                    key, e)
-                raise configexc.ValidationError(value, msg)
-
-            try:
-                val.encode('ascii')
-            except UnicodeEncodeError as e:
-                msg = "Value {!r} contains non-ascii characters: {}".format(
-                    val, e)
-                raise configexc.ValidationError(value, msg)
-
+            self._validate_str(key, 'key')
+            self._validate_str(val, 'value')
 
     def transform(self, value):
         if not value: