Implement builtin.next and py.IsException

Author: ncw

builtin/builtin.go

@@ -44,7 +44,7 @@ func init() {
 		// py.NewMethod("locals", builtin_locals, py.METH_NOARGS, locals_doc),
 		// py.NewMethod("max", builtin_max, 0, max_doc),
 		// py.NewMethod("min", builtin_min, 0, min_doc),
-		// py.NewMethod("next", builtin_next, 0, next_doc),
+		py.NewMethod("next", builtin_next, 0, next_doc),
 		// py.NewMethod("oct", builtin_oct, 0, oct_doc),
 		// py.NewMethod("ord", builtin_ord, 0, ord_doc),
 		py.NewMethod("pow", builtin_pow, 0, pow_doc),
@@ -301,3 +301,30 @@ func builtin___build_class__(self py.Object, args py.Tuple, kwargs py.StringDict
 	fmt.Printf("Globals = %v, Locals = %v\n", fn.Globals, ns)
 	return cls
 }
+
+const next_doc = `next(iterator[, default])
+
+Return the next item from the iterator. If default is given and the iterator
+is exhausted, it is returned instead of raising StopIteration.`
+
+func builtin_next(self py.Object, args py.Tuple) (res py.Object) {
+	var it, def py.Object
+
+	py.UnpackTuple(args, nil, "next", 1, 2, &it, &def)
+
+	if def != nil {
+		defer func() {
+			if r := recover(); r != nil {
+				if py.IsException(py.StopIteration, r) {
+					// Return defult on StopIteration
+					res = def
+				} else {
+					// Re-raise
+					panic(r)
+				}
+			}
+		}()
+	}
+
+	return py.Next(it)
+}

py/exception.go

@@ -253,6 +253,33 @@ func ExceptionGivenMatches(err, exc Object) bool {
 	return err == exc
 }
 
+// IsException matches the result of recover to an exception
+//
+// For use to catch a single python exception from go code
+//
+// It can be an instance or the class itself
+func IsException(exception *Type, r interface{}) bool {
+	var t *Type
+	switch ex := r.(type) {
+	case *Exception:
+		t = ex.Type()
+	case *Type:
+		t = ex
+	default:
+		return false
+	}
+	// Exact instance or subclass match
+	if t == exception {
+		return true
+	}
+	// Can't be a subclass of exception
+	if t.Flags&TPFLAGS_BASE_EXC_SUBCLASS == 0 {
+		return false
+	}
+	// Now the full match
+	return t.IsSubtype(exception)
+}
+
 // Check Interfaces
 var _ error = (*Exception)(nil)
 var _ error = (*ExceptionInfo)(nil)

vm/eval.go

@@ -117,12 +117,8 @@ func (vm *Vm) CheckException() {
 //
 // Otherwise deals with the as per vm.CheckException and returns false
 func (vm *Vm) catchStopIteration(r interface{}) bool {
-	// FIXME match subclasses of StopIteration too?
-	if ex, ok := r.(*py.Exception); ok && ex.Type() == py.StopIteration {
-		// StopIteration() raised
-		return true
-	} else if ex, ok := r.(*py.Type); ok && ex == py.StopIteration {
-		// StopIteration raised
+	if py.IsException(py.StopIteration, r) {
+		// StopIteration or subclass raises
 		return true
 	} else {
 		// Deal with the exception as normal