Add vm.is_callable

vm/src/builtins.rs

@@ -67,8 +67,8 @@ fn builtin_bin(x: PyIntRef, _vm: &VirtualMachine) -> String {
 
 // builtin_breakpoint
 
-fn builtin_callable(obj: PyObjectRef, _vm: &VirtualMachine) -> bool {
-    objtype::class_has_attr(&obj.class(), "__call__")
+fn builtin_callable(obj: PyObjectRef, vm: &VirtualMachine) -> bool {
+    vm.is_callable(&obj)
 }
 
 fn builtin_chr(i: u32, _vm: &VirtualMachine) -> String {

vm/src/vm.rs

@@ -666,6 +666,21 @@ impl VirtualMachine {
         crate::stdlib::json::de_pyobject(self, s)
     }
 
+    pub fn is_callable(&self, obj: &PyObjectRef) -> bool {
+        match_class!(obj,
+            PyFunction => true,
+            PyMethod => true,
+            PyBuiltinFunction => true,
+            obj => {
+                if let Some(dict) = &obj.dict {
+                    dict.contains_key("__call__", self)
+                } else {
+                    false
+                }
+            },
+        )
+    }
+
     pub fn _sub(&self, a: PyObjectRef, b: PyObjectRef) -> PyResult {
         self.call_or_reflection(a, b, "__sub__", "__rsub__", |vm, a, b| {
             Err(vm.new_unsupported_operand_error(a, b, "-"))