@@ -80,7 +80,9 @@ impl PyMappingProxy {
         match &self.mapping {
             MappingProxyInner::Class(class) => {
                 let key = PyStrRef::try_from_object(vm, key)?;
-                Ok(vm.ctx.new_bool(class.has_attr(key.as_str())))
+                Ok(vm
+                    .ctx
+                    .new_bool(class.attributes.read().contains_key(key.as_str())))
             }
             MappingProxyInner::Dict(obj) => vm._membership(obj.clone(), key),
         }
Original file line number	Diff line number	Diff line change
`@@ -80,7 +80,9 @@ impl PyMappingProxy {`
`80`	`80`	`match &self.mapping {`
`81`	`81`	`MappingProxyInner::Class(class) => {`
`82`	`82`	`let key = PyStrRef::try_from_object(vm, key)?;`
`83`		`- Ok(vm.ctx.new_bool(class.has_attr(key.as_str())))`
	`83`	`+ Ok(vm`
	`84`	`+ .ctx`
	`85`	`+ .new_bool(class.attributes.read().contains_key(key.as_str())))`
`84`	`86`	`}`
`85`	`87`	`MappingProxyInner::Dict(obj) => vm._membership(obj.clone(), key),`
`86`	`88`	`}`